path: root/security/commoncap.c (follow)
AgeCommit message (Collapse)AuthorFilesLines
2019-07-09Merge branch 'next-lsm' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-securityLinus Torvalds1-3/+3
Pull capabilities update from James Morris: "Minor fixes for capabilities: - Update the commoncap.c code to utilize XATTR_SECURITY_PREFIX_LEN, from Carmeli tamir. - Make the capability hooks static, from Yue Haibing" * 'next-lsm' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: security/commoncap: Use xattr security prefix len security: Make capability_hooks static
2019-07-07security/commoncap: Use xattr security prefix lenCarmeli Tamir1-2/+2
Using the existing defined XATTR_SECURITY_PREFIX_LEN instead of sizeof(XATTR_SECURITY_PREFIX) - 1. Pretty simple cleanup. Signed-off-by: Carmeli Tamir <carmeli.tamir@gmail.com> Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2019-06-11security: Make capability_hooks staticYueHaibing1-1/+1
Fix sparse warning: security/commoncap.c:1347:27: warning: symbol 'capability_hooks' was not declared. Should it be static? Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: YueHaibing <yuehaibing@huawei.com> Signed-off-by: James Morris <jamorris@linux.microsoft.com>
2019-05-30treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152Thomas Gleixner1-6/+1
Based on 1 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license as published by the free software foundation either version 2 of the license or at your option any later version extracted by the scancode license scanner the SPDX license identifier GPL-2.0-or-later has been chosen to replace the boilerplate/reference in 3029 file(s). Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Allison Randal <allison@lohutok.net> Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-03-07Merge tag 'audit-pr-20190305' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/auditLinus Torvalds1-0/+2
Pull audit updates from Paul Moore: "A lucky 13 audit patches for v5.1. Despite the rather large diffstat, most of the changes are from two bug fix patches that move code from one Kconfig option to another. Beyond that bit of churn, the remaining changes are largely cleanups and bug-fixes as we slowly march towards container auditing. It isn't all boring though, we do have a couple of new things: file capabilities v3 support, and expanded support for filtering on filesystems to solve problems with remote filesystems. All changes pass the audit-testsuite. Please merge for v5.1" * tag 'audit-pr-20190305' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/audit: audit: mark expected switch fall-through audit: hide auditsc_get_stamp and audit_serial prototypes audit: join tty records to their syscall audit: remove audit_context when CONFIG_ AUDIT and not AUDITSYSCALL audit: remove unused actx param from audit_rule_match audit: ignore fcaps on umount audit: clean up AUDITSYSCALL prototypes and stubs audit: more filter PATH records keyed on filesystem magic audit: add support for fcaps v3 audit: move loginuid and sessionid from CONFIG_AUDITSYSCALL to CONFIG_AUDIT audit: add syscall information to CONFIG_CHANGE records audit: hand taken context to audit_kill_trees for syscall logging audit: give a clue what CONFIG_CHANGE op was involved
2019-02-25LSM: Update function documentation for cap_capableMicah Morton1-1/+1
This should have gone in with commit c1a85a00ea66cb6f0bd0f14e47c28c2b0999799f. Signed-off-by: Micah Morton <mortonm@chromium.org> Signed-off-by: James Morris <james.morris@microsoft.com>
2019-01-25audit: add support for fcaps v3Richard Guy Briggs1-0/+2
V3 namespaced file capabilities were introduced in commit 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Add support for these by adding the "frootid" field to the existing fcaps fields in the NAME and BPRM_FCAPS records. Please see github issue https://github.com/linux-audit/audit-kernel/issues/103 Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Acked-by: Serge Hallyn <serge@hallyn.com> [PM: comment tweak to fit an 80 char line width] Signed-off-by: Paul Moore <paul@paul-moore.com>
2019-01-10LSM: generalize flag passing to security_capableMicah Morton1-8/+9
This patch provides a general mechanism for passing flags to the security_capable LSM hook. It replaces the specific 'audit' flag that is used to tell security_capable whether it should log an audit message for the given capability check. The reason for generalizing this flag passing is so we can add an additional flag that signifies whether security_capable is being called by a setid syscall (which is needed by the proposed SafeSetID LSM). Signed-off-by: Micah Morton <mortonm@chromium.org> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.morris@microsoft.com>
2019-01-08capability: Initialize as LSM_ORDER_FIRSTKees Cook1-1/+8
This converts capabilities to use the new LSM_ORDER_FIRST position. Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
2018-12-12security: audit and remove any unnecessary uses of module.hPaul Gortmaker1-1/+0
Historically a lot of these existed because we did not have a distinction between what was modular code and what was providing support to modules via EXPORT_SYMBOL and friends. That changed when we forked out support for the latter into the export.h file. This means we should be able to reduce the usage of module.h in code that is obj-y Makefile or bool Kconfig. The advantage in removing such instances is that module.h itself sources about 15 other headers; adding significantly to what we feed cpp, and it can obscure what headers we are effectively using. Since module.h might have been the implicit source for init.h (for __init) and for export.h (for EXPORT_SYMBOL) we consider each instance for the presence of either and replace as needed. Cc: James Morris <jmorris@namei.org> Cc: "Serge E. Hallyn" <serge@hallyn.com> Cc: John Johansen <john.johansen@canonical.com> Cc: Mimi Zohar <zohar@linux.ibm.com> Cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com> Cc: David Howells <dhowells@redhat.com> Cc: linux-security-module@vger.kernel.org Cc: linux-integrity@vger.kernel.org Cc: keyrings@vger.kernel.org Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: James Morris <james.morris@microsoft.com>
2018-09-04Merge tag 'v4.19-rc2' into next-generalJames Morris1-1/+1
Sync to Linux 4.19-rc2 for downstream developers.
2018-08-29security/capabilities: remove check for -EINVALChristian Brauner1-3/+0
bprm_caps_from_vfs_caps() never returned -EINVAL so remove the rc == -EINVAL check. Signed-off-by: Christian Brauner <christian@brauner.io> Reviewed-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: James Morris <james.morris@microsoft.com>
2018-08-11cap_inode_getsecurity: use d_find_any_alias() instead of d_find_alias()Eddie.Horng1-1/+1
The code in cap_inode_getsecurity(), introduced by commit 8db6c34f1dbc ("Introduce v3 namespaced file capabilities"), should use d_find_any_alias() instead of d_find_alias() do handle unhashed dentry correctly. This is needed, for example, if execveat() is called with an open but unlinked overlayfs file, because overlayfs unhashes dentry on unlink. This is a regression of real life application, first reported at https://www.spinics.net/lists/linux-unionfs/msg05363.html Below reproducer and setup can reproduce the case. const char* exec="echo"; const char *newargv[] = { "echo", "hello", NULL}; const char *newenviron[] = { NULL }; int fd, err; fd = open(exec, O_PATH); unlink(exec); err = syscall(322/*SYS_execveat*/, fd, "", newargv, newenviron, AT_EMPTY_PATH); if(err<0) fprintf(stderr, "execveat: %s\n", strerror(errno)); gcc compile into ~/test/a.out mount -t overlay -orw,lowerdir=/mnt/l,upperdir=/mnt/u,workdir=/mnt/w none /mnt/m cd /mnt/m cp /bin/echo . ~/test/a.out Expected result: hello Actually result: execveat: Invalid argument dmesg: Invalid argument reading file caps for /dev/fd/3 The 2nd reproducer and setup emulates similar case but for regular filesystem: const char* exec="echo"; int fd, err; char buf[256]; fd = open(exec, O_RDONLY); unlink(exec); err = fgetxattr(fd, "security.capability", buf, 256); if(err<0) fprintf(stderr, "fgetxattr: %s\n", strerror(errno)); gcc compile into ~/test_fgetxattr cd /tmp cp /bin/echo . ~/test_fgetxattr Result: fgetxattr: Invalid argument On regular filesystem, for example, ext4 read xattr from disk and return to execveat(), will not trigger this issue, however, the overlay attr handler pass real dentry to vfs_getxattr() will. This reproducer calls fgetxattr() with an unlinked fd, involkes vfs_getxattr() then reproduced the case that d_find_alias() in cap_inode_getsecurity() can't find the unlinked dentry. Suggested-by: Amir Goldstein <amir73il@gmail.com> Acked-by: Amir Goldstein <amir73il@gmail.com> Acked-by: Serge E. Hallyn <serge@hallyn.com> Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Cc: <stable@vger.kernel.org> # v4.14 Signed-off-by: Eddie Horng <eddie.horng@mediatek.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2018-05-24capabilities: Allow privileged user in s_user_ns to set security.* xattrsEric W. Biederman1-2/+6
A privileged user in s_user_ns will generally have the ability to manipulate the backing store and insert security.* xattrs into the filesystem directly. Therefore the kernel must be prepared to handle these xattrs from unprivileged mounts, and it makes little sense for commoncap to prevent writing these xattrs to the filesystem. The capability and LSM code have already been updated to appropriately handle xattrs from unprivileged mounts, so it is safe to loosen this restriction on setting xattrs. The exception to this logic is that writing xattrs to a mounted filesystem may also cause the LSM inode_post_setxattr or inode_setsecurity callbacks to be invoked. SELinux will deny the xattr update by virtue of applying mountpoint labeling to unprivileged userns mounts, and Smack will deny the writes for any user without global CAP_MAC_ADMIN, so loosening the capability check in commoncap is safe in this respect as well. Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: Serge Hallyn <serge@hallyn.com> Acked-by: Christian Brauner <christian@brauner.io> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2018-04-10commoncap: Handle memory allocation failure.Tetsuo Handa1-0/+2
syzbot is reporting NULL pointer dereference at xattr_getsecurity() [1], for cap_inode_getsecurity() is returning sizeof(struct vfs_cap_data) when memory allocation failed. Return -ENOMEM if memory allocation failed. [1] https://syzkaller.appspot.com/bug?id=a55ba438506fe68649a5f50d2d82d56b365e0107 Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Fixes: 8db6c34f1dbc8e06 ("Introduce v3 namespaced file capabilities") Reported-by: syzbot <syzbot+9369930ca44f29e60e2d@syzkaller.appspotmail.com> Cc: stable <stable@vger.kernel.org> # 4.14+ Acked-by: Serge E. Hallyn <serge@hallyn.com> Acked-by: James Morris <james.morris@microsoft.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2018-01-02capabilities: fix buffer overread on very short xattrEric Biggers1-12/+9
If userspace attempted to set a "security.capability" xattr shorter than 4 bytes (e.g. 'setfattr -n security.capability -v x file'), then cap_convert_nscap() read past the end of the buffer containing the xattr value because it accessed the ->magic_etc field without verifying that the xattr value is long enough to contain that field. Fix it by validating the xattr value size first. This bug was found using syzkaller with KASAN. The KASAN report was as follows (cleaned up slightly): BUG: KASAN: slab-out-of-bounds in cap_convert_nscap+0x514/0x630 security/commoncap.c:498 Read of size 4 at addr ffff88002d8741c0 by task syz-executor1/2852 CPU: 0 PID: 2852 Comm: syz-executor1 Not tainted 4.15.0-rc6-00200-gcc0aac99d977 #253 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0xe3/0x195 lib/dump_stack.c:53 print_address_description+0x73/0x260 mm/kasan/report.c:252 kasan_report_error mm/kasan/report.c:351 [inline] kasan_report+0x235/0x350 mm/kasan/report.c:409 cap_convert_nscap+0x514/0x630 security/commoncap.c:498 setxattr+0x2bd/0x350 fs/xattr.c:446 path_setxattr+0x168/0x1b0 fs/xattr.c:472 SYSC_setxattr fs/xattr.c:487 [inline] SyS_setxattr+0x36/0x50 fs/xattr.c:483 entry_SYSCALL_64_fastpath+0x18/0x85 Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Cc: <stable@vger.kernel.org> # v4.14+ Signed-off-by: Eric Biggers <ebiggers@google.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-11-13Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-securityLinus Torvalds1-65/+128
Pull general security subsystem updates from James Morris: "TPM (from Jarkko): - essential clean up for tpm_crb so that ARM64 and x86 versions do not distract each other as much as before - /dev/tpm0 rejects now too short writes (shorter buffer than specified in the command header - use DMA-safe buffer in tpm_tis_spi - otherwise mostly minor fixes. Smack: - base support for overlafs Capabilities: - BPRM_FCAPS fixes, from Richard Guy Briggs: The audit subsystem is adding a BPRM_FCAPS record when auditing setuid application execution (SYSCALL execve). This is not expected as it was supposed to be limited to when the file system actually had capabilities in an extended attribute. It lists all capabilities making the event really ugly to parse what is happening. The PATH record correctly records the setuid bit and owner. Suppress the BPRM_FCAPS record on set*id. TOMOYO: - Y2038 timestamping fixes" * 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: (28 commits) MAINTAINERS: update the IMA, EVM, trusted-keys, encrypted-keys entries Smack: Base support for overlayfs MAINTAINERS: remove David Safford as maintainer for encrypted+trusted keys tomoyo: fix timestamping for y2038 capabilities: audit log other surprising conditions capabilities: fix logic for effective root or real root capabilities: invert logic for clarity capabilities: remove a layer of conditional logic capabilities: move audit log decision to function capabilities: use intuitive names for id changes capabilities: use root_priveleged inline to clarify logic capabilities: rename has_cap to has_fcap capabilities: intuitive names for cap gain status capabilities: factor out cap_bprm_set_creds privileged root tpm, tpm_tis: use ARRAY_SIZE() to define TPM_HID_USR_IDX tpm: fix duplicate inline declaration specifier tpm: fix type of a local variables in tpm_tis_spi.c tpm: fix type of a local variable in tpm2_map_command() tpm: fix type of a local variable in tpm2_get_cc_attrs_tbl() tpm-dev-common: Reject too short writes ...
2017-10-20capabilities: audit log other surprising conditionsRichard Guy Briggs1-7/+22
The existing condition tested for process effective capabilities set by file attributes but intended to ignore the change if the result was unsurprisingly an effective full set in the case root is special with a setuid root executable file and we are root. Stated again: - When you execute a setuid root application, it is no surprise and expected that it got all capabilities, so we do not want capabilities recorded. if (pE_grew && !(pE_fullset && (eff_root || real_root) && root_priveleged) ) Now make sure we cover other cases: - If something prevented a setuid root app getting all capabilities and it wound up with one capability only, then it is a surprise and should be logged. When it is a setuid root file, we only want capabilities when the process does not get full capabilities.. root_priveleged && setuid_root && !pE_fullset - Similarly if a non-setuid program does pick up capabilities due to file system based capabilities, then we want to know what capabilities were picked up. When it has file system based capabilities we want the capabilities. !is_setuid && (has_fcap && pP_gained) - If it is a non-setuid file and it gets ambient capabilities, we want the capabilities. !is_setuid && pA_gained - These last two are combined into one due to the common first parameter. Related: https://github.com/linux-audit/audit-kernel/issues/16 Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: fix logic for effective root or real rootRichard Guy Briggs1-3/+2
Now that the logic is inverted, it is much easier to see that both real root and effective root conditions had to be met to avoid printing the BPRM_FCAPS record with audit syscalls. This meant that any setuid root applications would print a full BPRM_FCAPS record when it wasn't necessary, cluttering the event output, since the SYSCALL and PATH records indicated the presence of the setuid bit and effective root user id. Require only one of effective root or real root to avoid printing the unnecessary record. Ref: commit 3fc689e96c0c ("Add audit_log_bprm_fcaps/AUDIT_BPRM_FCAPS") See: https://github.com/linux-audit/audit-kernel/issues/16 Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: invert logic for clarityRichard Guy Briggs1-4/+4
The way the logic was presented, it was awkward to read and verify. Invert the logic using DeMorgan's Law to be more easily able to read and understand. Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: remove a layer of conditional logicRichard Guy Briggs1-13/+10
Remove a layer of conditional logic to make the use of conditions easier to read and analyse. Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: move audit log decision to functionRichard Guy Briggs1-20/+30
Move the audit log decision logic to its own function to isolate the complexity in one place. Suggested-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: use intuitive names for id changesRichard Guy Briggs1-6/+22
Introduce a number of inlines to make the use of the negation of uid_eq() easier to read and analyse. Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: use root_priveleged inline to clarify logicRichard Guy Briggs1-2/+4
Introduce inline root_privileged() to make use of SECURE_NONROOT easier to read. Suggested-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: rename has_cap to has_fcapRichard Guy Briggs1-10/+10
Rename has_cap to has_fcap to clarify it applies to file capabilities since the entire source file is about capabilities. Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: intuitive names for cap gain statusRichard Guy Briggs1-7/+11
Introduce macros cap_gained, cap_grew, cap_full to make the use of the negation of is_subset() easier to read and analyse. Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-20capabilities: factor out cap_bprm_set_creds privileged rootRichard Guy Briggs1-28/+48
Factor out the case of privileged root from the function cap_bprm_set_creds() to make the latter easier to read and analyse. Suggested-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: Richard Guy Briggs <rgb@redhat.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Kees Cook <keescook@chromium.org> Okay-ished-by: Paul Moore <paul@paul-moore.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-10-19commoncap: move assignment of fs_ns to avoid null pointer dereferenceColin Ian King1-1/+2
The pointer fs_ns is assigned from inode->i_ib->s_user_ns before a null pointer check on inode, hence if inode is actually null we will get a null pointer dereference on this assignment. Fix this by only dereferencing inode after the null pointer check on inode. Detected by CoverityScan CID#1455328 ("Dereference before null check") Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Signed-off-by: Colin Ian King <colin.king@canonical.com> Cc: stable@vger.kernel.org Acked-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-09-24Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-securityLinus Torvalds1-3/+3
Pull misc security layer update from James Morris: "This is the remaining 'general' change in the security tree for v4.14, following the direct merging of SELinux (+ TOMOYO), AppArmor, and seccomp. That's everything now for the security tree except IMA, which will follow shortly (I've been traveling for the past week with patchy internet)" * 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: security: fix description of values returned by cap_inode_need_killpriv
2017-09-23security: fix description of values returned by cap_inode_need_killprivStefan Berger1-3/+3
cap_inode_need_killpriv returns 1 if security.capability exists and has a value and inode_killpriv() is required, 0 otherwise. Fix the description of the return value to reflect this. Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com> Reviewed-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
2017-09-11Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespaceLinus Torvalds1-21/+256
Pull namespace updates from Eric Biederman: "Life has been busy and I have not gotten half as much done this round as I would have liked. I delayed it so that a minor conflict resolution with the mips tree could spend a little time in linux-next before I sent this pull request. This includes two long delayed user namespace changes from Kirill Tkhai. It also includes a very useful change from Serge Hallyn that allows the security capability attribute to be used inside of user namespaces. The practical effect of this is people can now untar tarballs and install rpms in user namespaces. It had been suggested to generalize this and encode some of the namespace information information in the xattr name. Upon close inspection that makes the things that should be hard easy and the things that should be easy more expensive. Then there is my bugfix/cleanup for signal injection that removes the magic encoding of the siginfo union member from the kernel internal si_code. The mips folks reported the case where I had used FPE_FIXME me is impossible so I have remove FPE_FIXME from mips, while at the same time including a return statement in that case to keep gcc from complaining about unitialized variables. I almost finished the work to get make copy_siginfo_to_user a trivial copy to user. The code is available at: git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git neuter-copy_siginfo_to_user-v3 But I did not have time/energy to get the code posted and reviewed before the merge window opened. I was able to see that the security excuse for just copying fields that we know are initialized doesn't work in practice there are buggy initializations that don't initialize the proper fields in siginfo. So we still sometimes copy unitialized data to userspace" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: Introduce v3 namespaced file capabilities mips/signal: In force_fcr31_sig return in the impossible case signal: Remove kernel interal si_code magic fcntl: Don't use ambiguous SIG_POLL si_codes prctl: Allow local CAP_SYS_ADMIN changing exe_file security: Use user_namespace::level to avoid redundant iterations in cap_capable() userns,pidns: Verify the userns for new pid namespaces signal/testing: Don't look for __SI_FAULT in userspace signal/mips: Document a conflict with SI_USER with SIGFPE signal/sparc: Document a conflict with SI_USER with SIGFPE signal/ia64: Document a conflict with SI_USER with SIGFPE signal/alpha: Document a conflict with SI_USER for SIGTRAP
2017-09-01Introduce v3 namespaced file capabilitiesSerge E. Hallyn1-19/+251
Root in a non-initial user ns cannot be trusted to write a traditional security.capability xattr. If it were allowed to do so, then any unprivileged user on the host could map his own uid to root in a private namespace, write the xattr, and execute the file with privilege on the host. However supporting file capabilities in a user namespace is very desirable. Not doing so means that any programs designed to run with limited privilege must continue to support other methods of gaining and dropping privilege. For instance a program installer must detect whether file capabilities can be assigned, and assign them if so but set setuid-root otherwise. The program in turn must know how to drop partial capabilities, and do so only if setuid-root. This patch introduces v3 of the security.capability xattr. It builds a vfs_ns_cap_data struct by appending a uid_t rootid to struct vfs_cap_data. This is the absolute uid_t (that is, the uid_t in user namespace which mounted the filesystem, usually init_user_ns) of the root id in whose namespaces the file capabilities may take effect. When a task asks to write a v2 security.capability xattr, if it is privileged with respect to the userns which mounted the filesystem, then nothing should change. Otherwise, the kernel will transparently rewrite the xattr as a v3 with the appropriate rootid. This is done during the execution of setxattr() to catch user-space-initiated capability writes. Subsequently, any task executing the file which has the noted kuid as its root uid, or which is in a descendent user_ns of such a user_ns, will run the file with capabilities. Similarly when asking to read file capabilities, a v3 capability will be presented as v2 if it applies to the caller's namespace. If a task writes a v3 security.capability, then it can provide a uid for the xattr so long as the uid is valid in its own user namespace, and it is privileged with CAP_SETFCAP over its namespace. The kernel will translate that rootid to an absolute uid, and write that to disk. After this, a task in the writer's namespace will not be able to use those capabilities (unless rootid was 0), but a task in a namespace where the given uid is root will. Only a single security.capability xattr may exist at a time for a given file. A task may overwrite an existing xattr so long as it is privileged over the inode. Note this is a departure from previous semantics, which required privilege to remove a security.capability xattr. This check can be re-added if deemed useful. This allows a simple setxattr to work, allows tar/untar to work, and allows us to tar in one namespace and untar in another while preserving the capability, without risking leaking privilege into a parent namespace. Example using tar: $ cp /bin/sleep sleepx $ mkdir b1 b2 $ lxc-usernsexec -m b:0:100000:1 -m b:1:$(id -u):1 -- chown 0:0 b1 $ lxc-usernsexec -m b:0:100001:1 -m b:1:$(id -u):1 -- chown 0:0 b2 $ lxc-usernsexec -m b:0:100000:1000 -- tar --xattrs-include=security.capability --xattrs -cf b1/sleepx.tar sleepx $ lxc-usernsexec -m b:0:100001:1000 -- tar --xattrs-include=security.capability --xattrs -C b2 -xf b1/sleepx.tar $ lxc-usernsexec -m b:0:100001:1000 -- getcap b2/sleepx b2/sleepx = cap_sys_admin+ep # /opt/ltp/testcases/bin/getv3xattr b2/sleepx v3 xattr, rootid is 100001 A patch to linux-test-project adding a new set of tests for this functionality is in the nsfscaps branch at github.com/hallyn/ltp Changelog: Nov 02 2016: fix invalid check at refuse_fcap_overwrite() Nov 07 2016: convert rootid from and to fs user_ns (From ebiederm: mar 28 2017) commoncap.c: fix typos - s/v4/v3 get_vfs_caps_from_disk: clarify the fs_ns root access check nsfscaps: change the code split for cap_inode_setxattr() Apr 09 2017: don't return v3 cap for caps owned by current root. return a v2 cap for a true v2 cap in non-init ns Apr 18 2017: . Change the flow of fscap writing to support s_user_ns writing. . Remove refuse_fcap_overwrite(). The value of the previous xattr doesn't matter. Apr 24 2017: . incorporate Eric's incremental diff . move cap_convert_nscap to setxattr and simplify its usage May 8, 2017: . fix leaking dentry refcount in cap_inode_getsecurity Signed-off-by: Serge Hallyn <serge@hallyn.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2017-08-01commoncap: Move cap_elevated calculation into bprm_set_credsKees Cook1-42/+10
Instead of a separate function, open-code the cap_elevated test, which lets us entirely remove bprm->cap_effective (to use the local "effective" variable instead), and more accurately examine euid/egid changes via the existing local "is_setid". The following LTP tests were run to validate the changes: # ./runltp -f syscalls -s cap # ./runltp -f securebits # ./runltp -f cap_bounds # ./runltp -f filecaps All kernel selftests for capabilities and exec continue to pass as well. Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: James Morris <james.l.morris@oracle.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Andy Lutomirski <luto@kernel.org>
2017-08-01commoncap: Refactor to remove bprm_secureexec hookKees Cook1-4/+8
The commoncap implementation of the bprm_secureexec hook is the only LSM that depends on the final call to its bprm_set_creds hook (since it may be called for multiple files, it ignores bprm->called_set_creds). As a result, it cannot safely _clear_ bprm->secureexec since other LSMs may have set it. Instead, remove the bprm_secureexec hook by introducing a new flag to bprm specific to commoncap: cap_elevated. This is similar to cap_effective, but that is used for a specific subset of elevated privileges, and exists solely to track state from bprm_set_creds to bprm_secureexec. As such, it will be removed in the next patch. Here, set the new bprm->cap_elevated flag when setuid/setgid has happened from bprm_fill_uid() or fscapabilities have been prepared. This temporarily moves the bprm_secureexec hook to a static inline. The helper will be removed in the next patch; this makes the step easier to review and bisect, since this does not introduce any changes to inputs nor outputs to the "elevated privileges" calculation. The new flag is merged with the bprm->secureexec flag in setup_new_exec() since this marks the end of any further prepare_binprm() calls. Cc: Andy Lutomirski <luto@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Andy Lutomirski <luto@kernel.org> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Serge Hallyn <serge@hallyn.com>
2017-07-20security: Use user_namespace::level to avoid redundant iterations in cap_capable()Kirill Tkhai1-2/+5
When ns->level is not larger then cred->user_ns->level, then ns can't be cred->user_ns's descendant, and there is no a sense to search in parents. So, break the cycle earlier and skip needless iterations. v2: Change comment on suggested by Andy Lutomirski. Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2017-03-06security: mark LSM hooks as __ro_after_initJames Morris1-1/+1
Mark all of the registration hooks as __ro_after_init (via the __lsm_ro_after_init macro). Signed-off-by: James Morris <james.l.morris@oracle.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Acked-by: Kees Cook <keescook@chromium.org>
2017-02-23Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespaceLinus Torvalds1-2/+3
Pull namespace updates from Eric Biederman: "There is a lot here. A lot of these changes result in subtle user visible differences in kernel behavior. I don't expect anything will care but I will revert/fix things immediately if any regressions show up. From Seth Forshee there is a continuation of the work to make the vfs ready for unpriviled mounts. We had thought the previous changes prevented the creation of files outside of s_user_ns of a filesystem, but it turns we missed the O_CREAT path. Ooops. Pavel Tikhomirov and Oleg Nesterov worked together to fix a long standing bug in the implemenation of PR_SET_CHILD_SUBREAPER where only children that are forked after the prctl are considered and not children forked before the prctl. The only known user of this prctl systemd forks all children after the prctl. So no userspace regressions will occur. Holding earlier forked children to the same rules as later forked children creates a semantic that is sane enough to allow checkpoing of processes that use this feature. There is a long delayed change by Nikolay Borisov to limit inotify instances inside a user namespace. Michael Kerrisk extends the API for files used to maniuplate namespaces with two new trivial ioctls to allow discovery of the hierachy and properties of namespaces. Konstantin Khlebnikov with the help of Al Viro adds code that when a network namespace exits purges it's sysctl entries from the dcache. As in some circumstances this could use a lot of memory. Vivek Goyal fixed a bug with stacked filesystems where the permissions on the wrong inode were being checked. I continue previous work on ptracing across exec. Allowing a file to be setuid across exec while being ptraced if the tracer has enough credentials in the user namespace, and if the process has CAP_SETUID in it's own namespace. Proc files for setuid or otherwise undumpable executables are now owned by the root in the user namespace of their mm. Allowing debugging of setuid applications in containers to work better. A bug I introduced with permission checking and automount is now fixed. The big change is to mark the mounts that the kernel initiates as a result of an automount. This allows the permission checks in sget to be safely suppressed for this kind of mount. As the permission check happened when the original filesystem was mounted. Finally a special case in the mount namespace is removed preventing unbounded chains in the mount hash table, and making the semantics simpler which benefits CRIU. The vfs fix along with related work in ima and evm I believe makes us ready to finish developing and merge fully unprivileged mounts of the fuse filesystem. The cleanups of the mount namespace makes discussing how to fix the worst case complexity of umount. The stacked filesystem fixes pave the way for adding multiple mappings for the filesystem uids so that efficient and safer containers can be implemented" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: proc/sysctl: Don't grab i_lock under sysctl_lock. vfs: Use upper filesystem inode in bprm_fill_uid() proc/sysctl: prune stale dentries during unregistering mnt: Tuck mounts under others instead of creating shadow/side mounts. prctl: propagate has_child_subreaper flag to every descendant introduce the walk_process_tree() helper nsfs: Add an ioctl() to return owner UID of a userns fs: Better permission checking for submounts exit: fix the setns() && PR_SET_CHILD_SUBREAPER interaction vfs: open() with O_CREAT should not create inodes with unknown ids nsfs: Add an ioctl() to return the namespace type proc: Better ownership of files for non-dumpable tasks in user namespaces exec: Remove LSM_UNSAFE_PTRACE_CAP exec: Test the ptracer's saved cred to see if the tracee can gain caps exec: Don't reset euid and egid when the tracee has CAP_SETUID inotify: Convert to using per-namespace limits
2017-01-24exec: Remove LSM_UNSAFE_PTRACE_CAPEric W. Biederman1-1/+1
With previous changes every location that tests for LSM_UNSAFE_PTRACE_CAP also tests for LSM_UNSAFE_PTRACE making the LSM_UNSAFE_PTRACE_CAP redundant, so remove it. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2017-01-24exec: Test the ptracer's saved cred to see if the tracee can gain capsEric W. Biederman1-1/+2
Now that we have user namespaces and non-global capabilities verify the tracer has capabilities in the relevant user namespace instead of in the current_user_ns(). As the test for setting LSM_UNSAFE_PTRACE_CAP is currently ptracer_capable(p, current_user_ns()) and the new task credentials are in current_user_ns() this change does not have any user visible change and simply moves the test to where it is used, making the code easier to read. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2017-01-24exec: Don't reset euid and egid when the tracee has CAP_SETUIDEric W. Biederman1-1/+1
Don't reset euid and egid when the tracee has CAP_SETUID in it's user namespace. I punted on relaxing this permission check long ago but now that I have read this code closely it is clear it is safe to test against CAP_SETUID in the user namespace. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2017-01-19LSM: Add /sys/kernel/security/lsmCasey Schaufler1-1/+2
I am still tired of having to find indirect ways to determine what security modules are active on a system. I have added /sys/kernel/security/lsm, which contains a comma separated list of the active security modules. No more groping around in /proc/filesystems or other clever hacks. Unchanged from previous versions except for being updated to the latest security next branch. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Acked-by: John Johansen <john.johansen@canonical.com> Acked-by: Paul Moore <paul@paul-moore.com> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
2016-10-07xattr: Add __vfs_{get,set,remove}xattr helpersAndreas Gruenbacher1-15/+10
Right now, various places in the kernel check for the existence of getxattr, setxattr, and removexattr inode operations and directly call those operations. Switch to helper functions and test for the IOP_XATTR flag instead. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Acked-by: James Morris <james.l.morris@oracle.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-06-24fs: Treat foreign mounts as nosuidAndy Lutomirski1-1/+7
If a process gets access to a mount from a different user namespace, that process should not be able to take advantage of setuid files or selinux entrypoints from that filesystem. Prevent this by treating mounts from other mount namespaces and those not owned by current_user_ns() or an ancestor as nosuid. This will make it safer to allow more complex filesystems to be mounted in non-root user namespaces. This does not remove the need for MNT_LOCK_NOSUID. The setuid, setgid, and file capability bits can no longer be abused if code in a user namespace were to clear nosuid on an untrusted filesystem, but this patch, by itself, is insufficient to protect the system from abuse of files that, when execed, would increase MAC privilege. As a more concrete explanation, any task that can manipulate a vfsmount associated with a given user namespace already has capabilities in that namespace and all of its descendents. If they can cause a malicious setuid, setgid, or file-caps executable to appear in that mount, then that executable will only allow them to elevate privileges in exactly the set of namespaces in which they are already privileges. On the other hand, if they can cause a malicious executable to appear with a dangerous MAC label, running it could change the caller's security context in a way that should not have been possible, even inside the namespace in which the task is confined. As a hardening measure, this would have made CVE-2014-5207 much more difficult to exploit. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2016-06-24fs: Limit file caps to the user namespace of the super blockSeth Forshee1-0/+2
Capability sets attached to files must be ignored except in the user namespaces where the mounter is privileged, i.e. s_user_ns and its descendants. Otherwise a vector exists for gaining privileges in namespaces where a user is not already privileged. Add a new helper function, current_in_user_ns(), to test whether a user namespace is the same as or a descendant of another namespace. Use this helper to determine whether a file's capability set should be applied to the caps constructed during exec. --EWB Replaced in_userns with the simpler current_in_userns. Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2016-05-17Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfsLinus Torvalds1-3/+3
Pull parallel filesystem directory handling update from Al Viro. This is the main parallel directory work by Al that makes the vfs layer able to do lookup and readdir in parallel within a single directory. That's a big change, since this used to be all protected by the directory inode mutex. The inode mutex is replaced by an rwsem, and serialization of lookups of a single name is done by a "in-progress" dentry marker. The series begins with xattr cleanups, and then ends with switching filesystems over to actually doing the readdir in parallel (switching to the "iterate_shared()" that only takes the read lock). A more detailed explanation of the process from Al Viro: "The xattr work starts with some acl fixes, then switches ->getxattr to passing inode and dentry separately. This is the point where the things start to get tricky - that got merged into the very beginning of the -rc3-based #work.lookups, to allow untangling the security_d_instantiate() mess. The xattr work itself proceeds to switch a lot of filesystems to generic_...xattr(); no complications there. After that initial xattr work, the series then does the following: - untangle security_d_instantiate() - convert a bunch of open-coded lookup_one_len_unlocked() to calls of that thing; one such place (in overlayfs) actually yields a trivial conflict with overlayfs fixes later in the cycle - overlayfs ended up switching to a variant of lookup_one_len_unlocked() sans the permission checks. I would've dropped that commit (it gets overridden on merge from #ovl-fixes in #for-next; proper resolution is to use the variant in mainline fs/overlayfs/super.c), but I didn't want to rebase the damn thing - it was fairly late in the cycle... - some filesystems had managed to depend on lookup/lookup exclusion for *fs-internal* data structures in a way that would break if we relaxed the VFS exclusion. Fixing hadn't been hard, fortunately. - core of that series - parallel lookup machinery, replacing ->i_mutex with rwsem, making lookup_slow() take it only shared. At that point lookups happen in parallel; lookups on the same name wait for the in-progress one to be done with that dentry. Surprisingly little code, at that - almost all of it is in fs/dcache.c, with fs/namei.c changes limited to lookup_slow() - making it use the new primitive and actually switching to locking shared. - parallel readdir stuff - first of all, we provide the exclusion on per-struct file basis, same as we do for read() vs lseek() for regular files. That takes care of most of the needed exclusion in readdir/readdir; however, these guys are trickier than lookups, so I went for switching them one-by-one. To do that, a new method '->iterate_shared()' is added and filesystems are switched to it as they are either confirmed to be OK with shared lock on directory or fixed to be OK with that. I hope to kill the original method come next cycle (almost all in-tree filesystems are switched already), but it's still not quite finished. - several filesystems get switched to parallel readdir. The interesting part here is dealing with dcache preseeding by readdir; that needs minor adjustment to be safe with directory locked only shared. Most of the filesystems doing that got switched to in those commits. Important exception: NFS. Turns out that NFS folks, with their, er, insistence on VFS getting the fuck out of the way of the Smart Filesystem Code That Knows How And What To Lock(tm) have grown the locking of their own. They had their own homegrown rwsem, with lookup/readdir/atomic_open being *writers* (sillyunlink is the reader there). Of course, with VFS getting the fuck out of the way, as requested, the actual smarts of the smart filesystem code etc. had become exposed... - do_last/lookup_open/atomic_open cleanups. As the result, open() without O_CREAT locks the directory only shared. Including the ->atomic_open() case. Backmerge from #for-linus in the middle of that - atomic_open() fix got brought in. - then comes NFS switch to saner (VFS-based ;-) locking, killing the homegrown "lookup and readdir are writers" kinda-sorta rwsem. All exclusion for sillyunlink/lookup is done by the parallel lookups mechanism. Exclusion between sillyunlink and rmdir is a real rwsem now - rmdir being the writer. Result: NFS lookups/readdirs/O_CREAT-less opens happen in parallel now. - the rest of the series consists of switching a lot of filesystems to parallel readdir; in a lot of cases ->llseek() gets simplified as well. One backmerge in there (again, #for-linus - rockridge fix)" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (74 commits) ext4: switch to ->iterate_shared() hfs: switch to ->iterate_shared() hfsplus: switch to ->iterate_shared() hostfs: switch to ->iterate_shared() hpfs: switch to ->iterate_shared() hpfs: handle allocation failures in hpfs_add_pos() gfs2: switch to ->iterate_shared() f2fs: switch to ->iterate_shared() afs: switch to ->iterate_shared() befs: switch to ->iterate_shared() befs: constify stuff a bit isofs: switch to ->iterate_shared() get_acorn_filename(): deobfuscate a bit btrfs: switch to ->iterate_shared() logfs: no need to lock directory in lseek switch ecryptfs to ->iterate_shared 9p: switch to ->iterate_shared() fat: switch to ->iterate_shared() romfs, squashfs: switch to ->iterate_shared() more trivial ->iterate_shared conversions ...
2016-04-22security: Introduce security_settime64()Baolin Wang1-1/+1
security_settime() uses a timespec, which is not year 2038 safe on 32bit systems. Thus this patch introduces the security_settime64() function with timespec64 type. We also convert the cap_settime() helper function to use the 64bit types. This patch then moves security_settime() to the header file as an inline helper function so that existing users can be iteratively converted. None of the existing hooks is using the timespec argument and therefor the patch is not making any functional changes. Cc: Serge Hallyn <serge.hallyn@canonical.com>, Cc: James Morris <james.l.morris@oracle.com>, Cc: "Serge E. Hallyn" <serge@hallyn.com>, Cc: Paul Moore <pmoore@redhat.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Kees Cook <keescook@chromium.org> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Reviewed-by: James Morris <james.l.morris@oracle.com> Signed-off-by: Baolin Wang <baolin.wang@linaro.org> [jstultz: Reworded commit message] Signed-off-by: John Stultz <john.stultz@linaro.org>
2016-04-11->getxattr(): pass dentry and inode as separate argumentsAl Viro1-3/+3
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-01-20ptrace: use fsuid, fsgid, effective creds for fs access checksJann Horn1-1/+6
By checking the effective credentials instead of the real UID / permitted capabilities, ensure that the calling process actually intended to use its credentials. To ensure that all ptrace checks use the correct caller credentials (e.g. in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS flag), use two new flags and require one of them to be set. The problem was that when a privileged task had temporarily dropped its privileges, e.g. by calling setreuid(0, user_uid), with the intent to perform following syscalls with the credentials of a user, it still passed ptrace access checks that the user would not be able to pass. While an attacker should not be able to convince the privileged task to perform a ptrace() syscall, this is a problem because the ptrace access check is reused for things in procfs. In particular, the following somewhat interesting procfs entries only rely on ptrace access checks: /proc/$pid/stat - uses the check for determining whether pointers should be visible, useful for bypassing ASLR /proc/$pid/maps - also useful for bypassing ASLR /proc/$pid/cwd - useful for gaining access to restricted directories that contain files with lax permissions, e.g. in this scenario: lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar drwx------ root root /root drwxr-xr-x root root /root/foobar -rw-r--r-- root root /root/foobar/secret Therefore, on a system where a root-owned mode 6755 binary changes its effective credentials as described and then dumps a user-specified file, this could be used by an attacker to reveal the memory layout of root's processes or reveal the contents of files he is not allowed to access (through /proc/$pid/cwd). [akpm@linux-foundation.org: fix warning] Signed-off-by: Jann Horn <jann@thejh.net> Acked-by: Kees Cook <keescook@chromium.org> Cc: Casey Schaufler <casey@schaufler-ca.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: James Morris <james.l.morris@oracle.com> Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Willy Tarreau <w@1wt.eu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04capabilities: add a securebit to disable PR_CAP_AMBIENT_RAISEAndy Lutomirski1-1/+2
Per Andrew Morgan's request, add a securebit to allow admins to disable PR_CAP_AMBIENT_RAISE. This securebit will prevent processes from adding capabilities to their ambient set. For simplicity, this disables PR_CAP_AMBIENT_RAISE entirely rather than just disabling setting previously cleared bits. Signed-off-by: Andy Lutomirski <luto@kernel.org> Acked-by: Andrew G. Morgan <morgan@kernel.org> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Cc: Kees Cook <keescook@chromium.org> Cc: Christoph Lameter <cl@linux.com> Cc: Serge Hallyn <serge.hallyn@canonical.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Aaron Jones <aaronmdjones@gmail.com> Cc: Ted Ts'o <tytso@mit.edu> Cc: Andrew G. Morgan <morgan@kernel.org> Cc: Mimi Zohar <zohar@linux.vnet.ibm.com> Cc: Austin S Hemmelgarn <ahferroin7@gmail.com> Cc: Markku Savela <msa@moth.iki.fi> Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: James Morris <james.l.morris@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04capabilities: ambient capabilitiesAndy Lutomirski1-10/+92
Credit where credit is due: this idea comes from Christoph Lameter with a lot of valuable input from Serge Hallyn. This patch is heavily based on Christoph's patch. ===== The status quo ===== On Linux, there are a number of capabilities defined by the kernel. To perform various privileged tasks, processes can wield capabilities that they hold. Each task has four capability masks: effective (pE), permitted (pP), inheritable (pI), and a bounding set (X). When the kernel checks for a capability, it checks pE. The other capability masks serve to modify what capabilities can be in pE. Any task can remove capabilities from pE, pP, or pI at any time. If a task has a capability in pP, it can add that capability to pE and/or pI. If a task has CAP_SETPCAP, then it can add any capability to pI, and it can remove capabilities from X. Tasks are not the only things that can have capabilities; files can also have capabilities. A file can have no capabilty information at all [1]. If a file has capability information, then it has a permitted mask (fP) and an inheritable mask (fI) as well as a single effective bit (fE) [2]. File capabilities modify the capabilities of tasks that execve(2) them. A task that successfully calls execve has its capabilities modified for the file ultimately being excecuted (i.e. the binary itself if that binary is ELF or for the interpreter if the binary is a script.) [3] In the capability evolution rules, for each mask Z, pZ represents the old value and pZ' represents the new value. The rules are: pP' = (X & fP) | (pI & fI) pI' = pI pE' = (fE ? pP' : 0) X is unchanged For setuid binaries, fP, fI, and fE are modified by a moderately complicated set of rules that emulate POSIX behavior. Similarly, if euid == 0 or ruid == 0, then fP, fI, and fE are modified differently (primary, fP and fI usually end up being the full set). For nonroot users executing binaries with neither setuid nor file caps, fI and fP are empty and fE is false. As an extra complication, if you execute a process as nonroot and fE is set, then the "secure exec" rules are in effect: AT_SECURE gets set, LD_PRELOAD doesn't work, etc. This is rather messy. We've learned that making any changes is dangerous, though: if a new kernel version allows an unprivileged program to change its security state in a way that persists cross execution of a setuid program or a program with file caps, this persistent state is surprisingly likely to allow setuid or file-capped programs to be exploited for privilege escalation. ===== The problem ===== Capability inheritance is basically useless. If you aren't root and you execute an ordinary binary, fI is zero, so your capabilities have no effect whatsoever on pP'. This means that you can't usefully execute a helper process or a shell command with elevated capabilities if you aren't root. On current kernels, you can sort of work around this by setting fI to the full set for most or all non-setuid executable files. This causes pP' = pI for nonroot, and inheritance works. No one does this because it's a PITA and it isn't even supported on most filesystems. If you try this, you'll discover that every nonroot program ends up with secure exec rules, breaking many things. This is a problem that has bitten many people who have tried to use capabilities for anything useful. ===== The proposed change ===== This patch adds a fifth capability mask called the ambient mask (pA). pA does what most people expect pI to do. pA obeys the invariant that no bit can ever be set in pA if it is not set in both pP and pI. Dropping a bit from pP or pI drops that bit from pA. This ensures that existing programs that try to drop capabilities still do so, with a complication. Because capability inheritance is so broken, setting KEEPCAPS, using setresuid to switch to nonroot uids, and then calling execve effectively drops capabilities. Therefore, setresuid from root to nonroot conditionally clears pA unless SECBIT_NO_SETUID_FIXUP is set. Processes that don't like this can re-add bits to pA afterwards. The capability evolution rules are changed: pA' = (file caps or setuid or setgid ? 0 : pA) pP' = (X & fP) | (pI & fI) | pA' pI' = pI pE' = (fE ? pP' : pA') X is unchanged If you are nonroot but you have a capability, you can add it to pA. If you do so, your children get that capability in pA, pP, and pE. For example, you can set pA = CAP_NET_BIND_SERVICE, and your children can automatically bind low-numbered ports. Hallelujah! Unprivileged users can create user namespaces, map themselves to a nonzero uid, and create both privileged (relative to their namespace) and unprivileged process trees. This is currently more or less impossible. Hallelujah! You cannot use pA to try to subvert a setuid, setgid, or file-capped program: if you execute any such program, pA gets cleared and the resulting evolution rules are unchanged by this patch. Users with nonzero pA are unlikely to unintentionally leak that capability. If they run programs that try to drop privileges, dropping privileges will still work. It's worth noting that the degree of paranoia in this patch could possibly be reduced without causing serious problems. Specifically, if we allowed pA to persist across executing non-pA-aware setuid binaries and across setresuid, then, naively, the only capabilities that could leak as a result would be the capabilities in pA, and any attacker *already* has those capabilities. This would make me nervous, though -- setuid binaries that tried to privilege-separate might fail to do so, and putting CAP_DAC_READ_SEARCH or CAP_DAC_OVERRIDE into pA could have unexpected side effects. (Whether these unexpected side effects would be exploitable is an open question.) I've therefore taken the more paranoid route. We can revisit this later. An alternative would be to require PR_SET_NO_NEW_PRIVS before setting ambient capabilities. I think that this would be annoying and would make granting otherwise unprivileged users minor ambient capabilities (CAP_NET_BIND_SERVICE or CAP_NET_RAW for example) much less useful than it is with this patch. ===== Footnotes ===== [1] Files that are missing the "security.capability" xattr or that have unrecognized values for that xattr end up with has_cap set to false. The code that does that appears to be complicated for no good reason. [2] The libcap capability mask parsers and formatters are dangerously misleading and the documentation is flat-out wrong. fE is *not* a mask; it's a single bit. This has probably confused every single person who has tried to use file capabilities. [3] Linux very confusingly processes both the script and the interpreter if applicable, for reasons that elude me. The results from thinking about a script's file capabilities and/or setuid bits are mostly discarded. Preliminary userspace code is here, but it needs updating: https://git.kernel.org/cgit/linux/kernel/git/luto/util-linux-playground.git/commit/?h=cap_ambient&id=7f5afbd175d2 Here is a test program that can be used to verify the functionality (from Christoph): /* * Test program for the ambient capabilities. This program spawns a shell * that allows running processes with a defined set of capabilities. * * (C) 2015 Christoph Lameter <cl@linux.com> * Released under: GPL v3 or later. * * * Compile using: * * gcc -o ambient_test ambient_test.o -lcap-ng * * This program must have the following capabilities to run properly: * Permissions for CAP_NET_RAW, CAP_NET_ADMIN, CAP_SYS_NICE * * A command to equip the binary with the right caps is: * * setcap cap_net_raw,cap_net_admin,cap_sys_nice+p ambient_test * * * To get a shell with additional caps that can be inherited by other processes: * * ./ambient_test /bin/bash * * * Verifying that it works: * * From the bash spawed by ambient_test run * * cat /proc/$$/status * * and have a look at the capabilities. */ #include <stdlib.h> #include <stdio.h> #include <errno.h> #include <cap-ng.h> #include <sys/prctl.h> #include <linux/capability.h> /* * Definitions from the kernel header files. These are going to be removed * when the /usr/include files have these defined. */ #define PR_CAP_AMBIENT 47 #define PR_CAP_AMBIENT_IS_SET 1 #define PR_CAP_AMBIENT_RAISE 2 #define PR_CAP_AMBIENT_LOWER 3 #define PR_CAP_AMBIENT_CLEAR_ALL 4 static void set_ambient_cap(int cap) { int rc; capng_get_caps_process(); rc = capng_update(CAPNG_ADD, CAPNG_INHERITABLE, cap); if (rc) { printf("Cannot add inheritable cap\n"); exit(2); } capng_apply(CAPNG_SELECT_CAPS); /* Note the two 0s at the end. Kernel checks for these */ if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, cap, 0, 0)) { perror("Cannot set cap"); exit(1); } } int main(int argc, char **argv) { int rc; set_ambient_cap(CAP_NET_RAW); set_ambient_cap(CAP_NET_ADMIN); set_ambient_cap(CAP_SYS_NICE); printf("Ambient_test forking shell\n"); if (execv(argv[1], argv + 1)) perror("Cannot exec"); return 0; } Signed-off-by: Christoph Lameter <cl@linux.com> # Original author Signed-off-by: Andy Lutomirski <luto@kernel.org> Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com> Acked-by: Kees Cook <keescook@chromium.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Aaron Jones <aaronmdjones@gmail.com> Cc: Ted Ts'o <tytso@mit.edu> Cc: Andrew G. Morgan <morgan@kernel.org> Cc: Mimi Zohar <zohar@linux.vnet.ibm.com> Cc: Austin S Hemmelgarn <ahferroin7@gmail.com> Cc: Markku Savela <msa@moth.iki.fi> Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: James Morris <james.l.morris@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>