bcachefs: Make snapshot_is_ancestor() safe

Snapshot table accesses generally need to be checking for invalid
snapshot ID now, fix one that was missed.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/snapshot.c b/fs/bcachefs/snapshot.c
index 0e806f04f3d7c5117ade3d612b1c851da243aead..544322d5c2517070143d367fa15d4ff353642556 100644 (file)
--- a/fs/bcachefs/snapshot.c
+++ b/fs/bcachefs/snapshot.c
@@ -125,6 +125,15 @@ static inline u32 get_ancestor_below(struct snapshot_table *t, u32 id, u32 ances
        return s->parent;
 }
 
+static bool test_ancestor_bitmap(struct snapshot_table *t, u32 id, u32 ancestor)
+{
+       const struct snapshot_t *s = __snapshot_t(t, id);
+       if (!s)
+               return false;
+
+       return test_bit(ancestor - id - 1, s->is_ancestor);
+}
+
 bool __bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
 {
        bool ret;
@@ -140,13 +149,11 @@ bool __bch2_snapshot_is_ancestor(struct bch_fs *c, u32 id, u32 ancestor)
        while (id && id < ancestor - IS_ANCESTOR_BITMAP)
                id = get_ancestor_below(t, id, ancestor);
 
-       if (id && id < ancestor) {
-               ret = test_bit(ancestor - id - 1, __snapshot_t(t, id)->is_ancestor);
+       ret = id && id < ancestor
+               ? test_ancestor_bitmap(t, id, ancestor)
+               : id == ancestor;
 
-               EBUG_ON(ret != __bch2_snapshot_is_ancestor_early(t, id, ancestor));
-       } else {
-               ret = id == ancestor;
-       }
+       EBUG_ON(ret != __bch2_snapshot_is_ancestor_early(t, id, ancestor));
 out:
        rcu_read_unlock();