do_move_mount(): fix an unsafe use of is_anon_ns()
What triggers it is a race between mount --move and umount -l
of the source; we should reject it (the source is parentless *and*
not the root of anon namespace at that), but the check for namespace
being an anon one is broken in that case - is_anon_ns() needs
ns to be non-NULL. Better fixed here than in is_anon_ns(), since
the rest of the callers is guaranteed to get a non-NULL argument...
Reported-by: syzbot+494c7ddf66acac0ad747@syzkaller.appspotmail.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index 3357c3d..ffb13f0 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2599,7 +2599,7 @@
if (attached && !check_mnt(old))
goto out;
- if (!attached && !is_anon_ns(ns))
+ if (!attached && !(ns && is_anon_ns(ns)))
goto out;
if (old->mnt.mnt_flags & MNT_LOCKED)
