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The current SECCOMP_RET_USER_NOTIF API allows for syscall supervision over
an fd. It is often used in settings where a supervising task emulates
syscalls on behalf of a supervised task in userspace, either to further
restrict the supervisee's syscall abilities or to circumvent kernel
enforced restrictions the supervisor deems safe to lift (e.g. actually
performing a mount(2) for an unprivileged container).
While SECCOMP_RET_USER_NOTIF allows for the interception of any syscall,
only a certain subset of syscalls could be correctly emulated. Over the
last few development cycles, the set of syscalls which can't be emulated
has been reduced due to the addition of pidfd_getfd(2). With this we are
now able to, for example, intercept syscalls that require the supervisor
to operate on file descriptors of the supervisee such as connect(2).
However, syscalls that cause new file descriptors to be installed can not
currently be correctly emulated since there is no way for the supervisor
to inject file descriptors into the supervisee. This patch adds a
new addfd ioctl to remove this restriction by allowing the supervisor to
install file descriptors into the intercepted task. By implementing this
feature via seccomp the supervisor effectively instructs the supervisee
to install a set of file descriptors into its own file descriptor table
during the intercepted syscall. This way it is possible to intercept
syscalls such as open() or accept(), and install (or replace, like
dup2(2)) the supervisor's resulting fd into the supervisee. One
replacement use-case would be to redirect the stdout and stderr of a
supervisee into log file descriptors opened by the supervisor.
The ioctl handling is based on the discussions[1] of how Extensible
Arguments should interact with ioctls. Instead of building size into
the addfd structure, make it a function of the ioctl command (which
is how sizes are normally passed to ioctls). To support forward and
backward compatibility, just mask out the direction and size, and match
everything. The size (and any future direction) checks are done along
with copy_struct_from_user() logic.
As a note, the seccomp_notif_addfd structure is laid out based on 8-byte
alignment without requiring packing as there have been packing issues
with uapi highlighted before[2][3]. Although we could overload the
newfd field and use -1 to indicate that it is not to be used, doing
so requires changing the size of the fd field, and introduces struct
packing complexity.
[1]: https://lore.kernel.org/lkml/87o8w9bcaf.fsf@mid.deneb.enyo.de/
[2]: https://lore.kernel.org/lkml/a328b91d-fd8f-4f27-b3c2-91a9c45f18c0@rasmusvillemoes.dk/
[3]: https://lore.kernel.org/lkml/20200612104629.GA15814@ircssh-2.c.rugged-nimbus-611.internal
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Tycho Andersen <tycho@tycho.ws>
Cc: Jann Horn <jannh@google.com>
Cc: Robert Sesek <rsesek@google.com>
Cc: Chris Palmer <palmer@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-api@vger.kernel.org
Suggested-by: Matt Denton <mpdenton@google.com>
Link: https://lore.kernel.org/r/20200603011044.7972-4-sargun@sargun.me
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Reviewed-by: Will Drewry <wad@chromium.org>
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
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Expand __receive_fd() with support for replace_fd() for the coming seccomp
"addfd" ioctl(). Add new wrapper receive_fd_replace() for the new behavior
and update existing wrappers to retain old behavior.
Thanks to Colin Ian King <colin.king@canonical.com> for pointing out an
uninitialized variable exposure in an earlier version of this patch.
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dmitry Kadashev <dkadashev@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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Replace the open-coded version of receive_fd() with a call to the
new helper.
Thanks to Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@gmail.com> for
catching a missed fput() in an earlier version of this patch.
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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For both pidfd and seccomp, the __user pointer is not used. Update
__receive_fd() to make writing to ufd optional via a NULL check. However,
for the receive_fd_user() wrapper, ufd is NULL checked so an -EFAULT
can be returned to avoid changing the SCM_RIGHTS interface behavior. Add
new wrapper receive_fd() for pidfd and seccomp that does not use the ufd
argument. For the new helper, the allocated fd needs to be returned on
success. Update the existing callers to handle it.
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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In preparation for users of the "install a received file" logic outside
of net/ (pidfd and seccomp), relocate and rename __scm_install_fd() from
net/core/scm.c to __receive_fd() in fs/file.c, and provide a wrapper
named receive_fd_user(), as future patches will change the interface
to __receive_fd().
Additionally add a comment to fd_install() as a counterpoint to how
__receive_fd() interacts with fput().
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Dmitry Kadashev <dkadashev@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Ido Schimmel <idosch@idosch.org>
Cc: Ioana Ciornei <ioana.ciornei@nxp.com>
Cc: linux-fsdevel@vger.kernel.org
Cc: netdev@vger.kernel.org
Reviewed-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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Duplicate the cleanups from commit 2618d530dd8b ("net/scm: cleanup
scm_detach_fds") into the compat code.
Replace open-coded __receive_sock() with a call to the helper.
Move the check added in commit 1f466e1f15cf ("net: cleanly handle kernel
vs user buffers for ->msg_control") to before the compat call, even
though it should be impossible for an in-kernel call to also be compat.
Correct the int "flags" argument to unsigned int to match fd_install()
and similar APIs.
Regularize any remaining differences, including a whitespace issue,
a checkpatch warning, and add the check from commit 6900317f5eff ("net,
scm: fix PaX detected msg_controllen overflow in scm_detach_fds") which
fixed an overflow unique to 64-bit. To avoid confusion when comparing
the compat handler to the native handler, just include the same check
in the compat handler.
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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The sock counting (sock_update_netprioidx() and sock_update_classid())
was missing from pidfd's implementation of received fd installation. Add
a call to the new __receive_sock() helper.
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: 8649c322f75c ("pid: Implement pidfd_getfd syscall")
Signed-off-by: Kees Cook <keescook@chromium.org>
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Add missed sock updates to compat path via a new helper, which will be
used more in coming patches. (The net/core/scm.c code is left as-is here
to assist with -stable backports for the compat path.)
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sargun Dhillon <sargun@sargun.me>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 48a87cc26c13 ("net: netprio: fd passed in SCM_RIGHTS datagram not set correctly")
Fixes: d84295067fc7 ("net: net_cls: fd passed in SCM_RIGHTS datagram not set correctly")
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
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There should be no difference between -1 and other negative syscalls
while tracing.
Cc: Keno Fischer <keno@juliacomputing.com>
Tested-by: Will Deacon <will@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
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Now that the selftest harness has variants, use them to eliminate a
bunch of copy/paste duplication.
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Tested-by: Will Deacon <will@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
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The FIXTURE*() macro kern-doc examples had the wrong names for the C code
examples associated with them. Fix those and clarify that FIXTURE_DATA()
usage should be avoided.
Cc: Shuah Khan <shuah@kernel.org>
Fixes: 74bc7c97fa88 ("kselftest: add fixture variants")
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
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The terminator for the mode 1 syscalls list was a 0, but that could be
a valid syscall number (e.g. x86_64 __NR_read). By luck, __NR_read was
listed first and the loop construct would not test it, so there was no
bug. However, this is fragile. Replace the terminator with -1 instead,
and make the variable name for mode 1 syscall lists more descriptive.
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
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When SECCOMP_IOCTL_NOTIF_ID_VALID was first introduced it had the wrong
direction flag set. While this isn't a big deal as nothing currently
enforces these bits in the kernel, it should be defined correctly. Fix
the define and provide support for the old command until it is no longer
needed for backward compatibility.
Fixes: 6a21cc50f0c7 ("seccomp: add a return code to trap to userspace")
Signed-off-by: Kees Cook <keescook@chromium.org>
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The user_trap_syscall() helper creates a filter with
SECCOMP_RET_USER_NOTIF. To avoid confusion with SECCOMP_RET_TRAP, rename
the helper to user_notif_syscall().
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@chromium.org>
Cc: linux-kselftest@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: bpf@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
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The seccomp tests are a bit noisy without CONFIG_CHECKPOINT_RESTORE (due
to missing the kcmp() syscall). The seccomp tests are more accurate with
kcmp(), but it's not strictly required. Refactor the tests to use
alternatives (comparing fd numbers), and provide a central test for
kcmp() so there is a single SKIP instead of many. Continue to produce
warnings for the other tests, though.
Additionally adds some more bad flag EINVAL tests to the addfd selftest.
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@chromium.org>
Cc: linux-kselftest@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: bpf@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
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Avoid open-coding "seccomp: " prefixes for pr_*() calls.
Signed-off-by: Kees Cook <keescook@chromium.org>
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The seccomp benchmark calibration loop did not need to take so long.
Instead, use a simple 1 second timeout and multiply up to target. It
does not need to be accurate.
Signed-off-by: Kees Cook <keescook@chromium.org>
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Sargun Dhillon
Kees Cook