fanotify: Taint on use of FANOTIFY_ACCESS_PERMISSIONS

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 258e8f63514841a9db81d80e31e6862a4d728845..d9ecaf8ee69fad8aa760bf0043fdc966fbe63204 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -868,6 +868,14 @@ SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
 #endif
                return -EINVAL;
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+       if (mask & FAN_ALL_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_USER, LOCKDEP_STILL_OK);
+       }
+#endif
+
        f = fdget(fanotify_fd);
        if (unlikely(!f.file))
                return -EBADF;