The sizes by which seccomp_notif and seccomp_notif_resp are allocated are
based on the SECCOMP_GET_NOTIF_SIZES ioctl. This allows for graceful
extension of these datastructures. If userspace zeroes out the
datastructure based on its version, and it is lagging behind the kernel's
version, it will end up sending trailing garbage. On the other hand,
if it is ahead of the kernel version, it will write extra zero space,
and potentially cause corruption.
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Suggested-by: Tycho Andersen <tycho@tycho.ws>
Link: https://lore.kernel.org/r/20191230203503.4925-1-sargun@sargun.me
Fixes: fec7b66905 ("samples: add an example of seccomp user trap")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
The idea here is just to give a demonstration of how one could safely use
the SECCOMP_RET_USER_NOTIF feature to do mount policies. This particular
policy is (as noted in the comment) not very interesting, but it serves to
illustrate how one might apply a policy dodging the various TOCTOU issues.
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
CC: Kees Cook <keescook@chromium.org>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Eric W. Biederman <ebiederm@xmission.com>
CC: "Serge E. Hallyn" <serge@hallyn.com>
CC: Christian Brauner <christian@brauner.io>
CC: Tyler Hicks <tyhicks@canonical.com>
CC: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
Signed-off-by: Kees Cook <keescook@chromium.org>
Sargun Dhillon