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authorDavid Howells <dhowells@redhat.com>2009-09-02 09:14:21 +0100
committerJames Morris <jmorris@namei.org>2009-09-02 21:29:22 +1000
commitee18d64c1f632043a02e6f5ba5e045bb26a5465f (patch)
tree80b5a4d530ec7d5fd69799920f0db7b78aba6b9d /security/keys/keyctl.c
parentKEYS: Extend TIF_NOTIFY_RESUME to (almost) all architectures [try #6] (diff)
downloadlinux-dev-ee18d64c1f632043a02e6f5ba5e045bb26a5465f.tar.xz
linux-dev-ee18d64c1f632043a02e6f5ba5e045bb26a5465f.zip
KEYS: Add a keyctl to install a process's session keyring on its parent [try #6]
Add a keyctl to install a process's session keyring onto its parent. This replaces the parent's session keyring. Because the COW credential code does not permit one process to change another process's credentials directly, the change is deferred until userspace next starts executing again. Normally this will be after a wait*() syscall. To support this, three new security hooks have been provided: cred_alloc_blank() to allocate unset security creds, cred_transfer() to fill in the blank security creds and key_session_to_parent() - which asks the LSM if the process may replace its parent's session keyring. The replacement may only happen if the process has the same ownership details as its parent, and the process has LINK permission on the session keyring, and the session keyring is owned by the process, and the LSM permits it. Note that this requires alteration to each architecture's notify_resume path. This has been done for all arches barring blackfin, m68k* and xtensa, all of which need assembly alteration to support TIF_NOTIFY_RESUME. This allows the replacement to be performed at the point the parent process resumes userspace execution. This allows the userspace AFS pioctl emulation to fully emulate newpag() and the VIOCSETTOK and VIOCSETTOK2 pioctls, all of which require the ability to alter the parent process's PAG membership. However, since kAFS doesn't use PAGs per se, but rather dumps the keys into the session keyring, the session keyring of the parent must be replaced if, for example, VIOCSETTOK is passed the newpag flag. This can be tested with the following program: #include <stdio.h> #include <stdlib.h> #include <keyutils.h> #define KEYCTL_SESSION_TO_PARENT 18 #define OSERROR(X, S) do { if ((long)(X) == -1) { perror(S); exit(1); } } while(0) int main(int argc, char **argv) { key_serial_t keyring, key; long ret; keyring = keyctl_join_session_keyring(argv[1]); OSERROR(keyring, "keyctl_join_session_keyring"); key = add_key("user", "a", "b", 1, keyring); OSERROR(key, "add_key"); ret = keyctl(KEYCTL_SESSION_TO_PARENT); OSERROR(ret, "KEYCTL_SESSION_TO_PARENT"); return 0; } Compiled and linked with -lkeyutils, you should see something like: [dhowells@andromeda ~]$ keyctl show Session Keyring -3 --alswrv 4043 4043 keyring: _ses 355907932 --alswrv 4043 -1 \_ keyring: _uid.4043 [dhowells@andromeda ~]$ /tmp/newpag [dhowells@andromeda ~]$ keyctl show Session Keyring -3 --alswrv 4043 4043 keyring: _ses 1055658746 --alswrv 4043 4043 \_ user: a [dhowells@andromeda ~]$ /tmp/newpag hello [dhowells@andromeda ~]$ keyctl show Session Keyring -3 --alswrv 4043 4043 keyring: hello 340417692 --alswrv 4043 4043 \_ user: a Where the test program creates a new session keyring, sticks a user key named 'a' into it and then installs it on its parent. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to '')
-rw-r--r--security/keys/keyctl.c102
1 files changed, 102 insertions, 0 deletions
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 736d7800f97f..74c968524592 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1228,6 +1228,105 @@ long keyctl_get_security(key_serial_t keyid,
return ret;
}
+/*
+ * attempt to install the calling process's session keyring on the process's
+ * parent process
+ * - the keyring must exist and must grant us LINK permission
+ * - implements keyctl(KEYCTL_SESSION_TO_PARENT)
+ */
+long keyctl_session_to_parent(void)
+{
+ struct task_struct *me, *parent;
+ const struct cred *mycred, *pcred;
+ struct cred *cred, *oldcred;
+ key_ref_t keyring_r;
+ int ret;
+
+ keyring_r = lookup_user_key(KEY_SPEC_SESSION_KEYRING, 0, KEY_LINK);
+ if (IS_ERR(keyring_r))
+ return PTR_ERR(keyring_r);
+
+ /* our parent is going to need a new cred struct, a new tgcred struct
+ * and new security data, so we allocate them here to prevent ENOMEM in
+ * our parent */
+ ret = -ENOMEM;
+ cred = cred_alloc_blank();
+ if (!cred)
+ goto error_keyring;
+
+ cred->tgcred->session_keyring = key_ref_to_ptr(keyring_r);
+ keyring_r = NULL;
+
+ me = current;
+ write_lock_irq(&tasklist_lock);
+
+ parent = me->real_parent;
+ ret = -EPERM;
+
+ /* the parent mustn't be init and mustn't be a kernel thread */
+ if (parent->pid <= 1 || !parent->mm)
+ goto not_permitted;
+
+ /* the parent must be single threaded */
+ if (atomic_read(&parent->signal->count) != 1)
+ goto not_permitted;
+
+ /* the parent and the child must have different session keyrings or
+ * there's no point */
+ mycred = current_cred();
+ pcred = __task_cred(parent);
+ if (mycred == pcred ||
+ mycred->tgcred->session_keyring == pcred->tgcred->session_keyring)
+ goto already_same;
+
+ /* the parent must have the same effective ownership and mustn't be
+ * SUID/SGID */
+ if (pcred-> uid != mycred->euid ||
+ pcred->euid != mycred->euid ||
+ pcred->suid != mycred->euid ||
+ pcred-> gid != mycred->egid ||
+ pcred->egid != mycred->egid ||
+ pcred->sgid != mycred->egid)
+ goto not_permitted;
+
+ /* the keyrings must have the same UID */
+ if (pcred ->tgcred->session_keyring->uid != mycred->euid ||
+ mycred->tgcred->session_keyring->uid != mycred->euid)
+ goto not_permitted;
+
+ /* the LSM must permit the replacement of the parent's keyring with the
+ * keyring from this process */
+ ret = security_key_session_to_parent(mycred, pcred,
+ key_ref_to_ptr(keyring_r));
+ if (ret < 0)
+ goto not_permitted;
+
+ /* if there's an already pending keyring replacement, then we replace
+ * that */
+ oldcred = parent->replacement_session_keyring;
+
+ /* the replacement session keyring is applied just prior to userspace
+ * restarting */
+ parent->replacement_session_keyring = cred;
+ cred = NULL;
+ set_ti_thread_flag(task_thread_info(parent), TIF_NOTIFY_RESUME);
+
+ write_unlock_irq(&tasklist_lock);
+ if (oldcred)
+ put_cred(oldcred);
+ return 0;
+
+already_same:
+ ret = 0;
+not_permitted:
+ put_cred(cred);
+ return ret;
+
+error_keyring:
+ key_ref_put(keyring_r);
+ return ret;
+}
+
/*****************************************************************************/
/*
* the key control system call
@@ -1313,6 +1412,9 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
(char __user *) arg3,
(size_t) arg4);
+ case KEYCTL_SESSION_TO_PARENT:
+ return keyctl_session_to_parent();
+
default:
return -EOPNOTSUPP;
}