bcachefs: Add checks for invalid snapshot IDs

Previously, we assumed that keys were consistent with the snapshots
btree - but that's not correct as fsck may not have been run or may not
be complete.

This adds checks and error handling when using the in-memory snapshots
table (that mirrors the snapshots btree).

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

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/bcachefs/data_update.c b/fs/bcachefs/data_update.c
index 4150feca42a2..b564404dad71 100644
--- a/fs/bcachefs/data_update.c
+++ b/fs/bcachefs/data_update.c
@@ -14,6 +14,7 @@
 #include "move.h"
 #include "nocow_locking.h"
 #include "rebalance.h"
+#include "snapshot.h"
 #include "subvolume.h"
 #include "trace.h"
 
@@ -509,6 +510,14 @@ int bch2_data_update_init(struct btree_trans *trans,
 	unsigned ptrs_locked = 0;
 	int ret = 0;
 
+	/*
+	 * fs is corrupt  we have a key for a snapshot node that doesn't exist,
+	 * and we have to check for this because we go rw before repairing the
+	 * snapshots table - just skip it, we can move it later.
+	 */
+	if (unlikely(k.k->p.snapshot && !bch2_snapshot_equiv(c, k.k->p.snapshot)))
+		return -BCH_ERR_data_update_done;
+
 	bch2_bkey_buf_init(&m->k);
 	bch2_bkey_buf_reassemble(&m->k, c, k);
 	m->btree_id	= btree_id;