diff options
| author | Tycho Andersen <tycho@tycho.ws> | 2020-03-04 11:05:17 -0700 |
|---|---|---|
| committer | Kees Cook <keescook@chromium.org> | 2020-03-04 14:48:54 -0800 |
| commit | 51891498f2da78ee64dfad88fa53c9e85fb50abf (patch) | |
| tree | 6a75fa013734d64980e797831cf123c69cab0c3f /kernel/seccomp.c | |
| parent | 11a48a5a18c63fd7621bb050228cebf13566e4d8 (diff) | |
| download | lwn-51891498f2da78ee64dfad88fa53c9e85fb50abf.tar.gz lwn-51891498f2da78ee64dfad88fa53c9e85fb50abf.zip | |
seccomp: allow TSYNC and USER_NOTIF together
The restriction introduced in 7a0df7fbc145 ("seccomp: Make NEW_LISTENER and
TSYNC flags exclusive") is mostly artificial: there is enough information
in a seccomp user notification to tell which thread triggered a
notification. The reason it was introduced is because TSYNC makes the
syscall return a thread-id on failure, and NEW_LISTENER returns an fd, and
there's no way to distinguish between these two cases (well, I suppose the
caller could check all fds it has, then do the syscall, and if the return
value was an fd that already existed, then it must be a thread id, but
bleh).
Matthew would like to use these two flags together in the Chrome sandbox
which wants to use TSYNC for video drivers and NEW_LISTENER to proxy
syscalls.
So, let's fix this ugliness by adding another flag, TSYNC_ESRCH, which
tells the kernel to just return -ESRCH on a TSYNC error. This way,
NEW_LISTENER (and any subsequent seccomp() commands that want to return
positive values) don't conflict with each other.
Suggested-by: Matthew Denton <mpdenton@google.com>
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Link: https://lore.kernel.org/r/20200304180517.23867-1-tycho@tycho.ws
Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'kernel/seccomp.c')
| -rw-r--r-- | kernel/seccomp.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/kernel/seccomp.c b/kernel/seccomp.c index b6ea3dcb57bf..29022c1bbe18 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -528,8 +528,12 @@ static long seccomp_attach_filter(unsigned int flags, int ret; ret = seccomp_can_sync_threads(); - if (ret) - return ret; + if (ret) { + if (flags & SECCOMP_FILTER_FLAG_TSYNC_ESRCH) + return -ESRCH; + else + return ret; + } } /* Set log flag, if present. */ @@ -1288,10 +1292,12 @@ static long seccomp_set_mode_filter(unsigned int flags, * In the successful case, NEW_LISTENER returns the new listener fd. * But in the failure case, TSYNC returns the thread that died. If you * combine these two flags, there's no way to tell whether something - * succeeded or failed. So, let's disallow this combination. + * succeeded or failed. So, let's disallow this combination if the user + * has not explicitly requested no errors from TSYNC. */ if ((flags & SECCOMP_FILTER_FLAG_TSYNC) && - (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER)) + (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) && + ((flags & SECCOMP_FILTER_FLAG_TSYNC_ESRCH) == 0)) return -EINVAL; /* Prepare the new filter before holding any locks. */ |