bcachefs: Add missing guard in bch2_snapshot_has_children()

We additionally need to be going inconsistent if passed an invalid
snapshot ID; that patch will need more thorough testing.

Reported-by: syzbot+1c9fca23fe478633b305@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/snapshot.h b/fs/bcachefs/snapshot.h
index bd5d74269d15a6e293dfe8455ed7f7b8c8aa6919..ab13d8f4b41e1e934c1b5f5c21975358df128019 100644 (file)
--- a/fs/bcachefs/snapshot.h
+++ b/fs/bcachefs/snapshot.h
@@ -176,12 +176,9 @@ static inline bool bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ances
 
 static inline bool bch2_snapshot_has_children(struct bch_fs *c, u32 id)
 {
-       const struct snapshot_t *t;
-       bool ret;
-
        rcu_read_lock();
-       t = snapshot_t(c, id);
-       ret = (t->children[0]|t->children[1]) != 0;
+       const struct snapshot_t *t = snapshot_t(c, id);
+       bool ret = t && (t->children[0]|t->children[1]) != 0;
        rcu_read_unlock();
 
        return ret;