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 9752e7270e616d3641ca0f4fe9b0dd90ccd1ef1c..dc0aa77acd57b825d7617bece9a0233f049b8b4c 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -863,6 +863,14 @@ 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;