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authorTycho Andersen <tycho@tycho.ws>2020-03-04 11:05:17 -0700
committerKees Cook <keescook@chromium.org>2020-03-04 14:48:54 -0800
commit51891498f2da78ee64dfad88fa53c9e85fb50abf (patch)
tree6a75fa013734d64980e797831cf123c69cab0c3f /kernel
parent11a48a5a18c63fd7621bb050228cebf13566e4d8 (diff)
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')
-rw-r--r--kernel/seccomp.c14
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. */