fanotify: Taint on use of FANOTIFY_ACCESS_PERMISSIONS

Forwarded: not-needed

Various free and proprietary AV products use this feature and users
apparently want it.  But punting access checks to userland seems like
an easy way to deadlock the system, and there will be nothing we can
do about that.  So warn and taint the kernel if this feature is
actually used.

Gbp-Pq: Topic debian
Gbp-Pq: Name fanotify-taint-on-use-of-fanotify_access_permissions.patch

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index a792e21c530993a0d721921ad945b65fcabc095d..cfd769caca714456266bc6cdd47a570fff9b0bed 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1563,6 +1563,14 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
        if (ignored)
                mask &= ~FANOTIFY_EVENT_FLAGS;
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+       if (mask & FANOTIFY_PERM_EVENTS) {
+               pr_warn_once("%s (%d): Using fanotify permission checks may lead to deadlock; tainting kernel\n",
+                            current->comm, current->pid);
+               add_taint(TAINT_AUX, LOCKDEP_STILL_OK);
+       }
+#endif
+
        f = fdget(fanotify_fd);
        if (unlikely(!f.file))
                return -EBADF;