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 ec4d8c59d0e379df56efef0c86d3d303326ff071..7e393ed0da2392959a776daa3da5610ebbfa075b 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -865,6 +865,14 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
        if (mask & ~valid_mask)
                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;