[PATCH v3] bcachefs: Fix NULL ptr dereference in btree_node_iter_and_journal_peek

From: Piotr Zalewski
Date: Sun Oct 27 2024 - 15:47:12 EST


Add NULL check for key returned from bch2_btree_and_journal_iter_peek in
btree_node_iter_and_journal_peek to avoid NULL ptr dereference in
bch2_bkey_buf_reassemble.

When key returned from bch2_btree_and_journal_iter_peek is NULL it means
that btree topology needs repair. Print topology error message with
position at which node wasn't found, its parent node information and
btree_id with level.

Return error code returned by bch2_topology_error to ensure that topology
error is handled properly by recovery.

Reported-by: syzbot+005ef9aa519f30d97657@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=005ef9aa519f30d97657
Fixes: 5222a4607cd8 ("bcachefs: BTREE_ITER_WITH_JOURNAL")
Suggested-by: Alan Huang <mmpgouride@xxxxxxxxx>
Suggested-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Piotr Zalewski <pZ010001011111@xxxxxxxxx>
---

Notes:
changes in v3:
- add btree_id and level info to the error message.
- use bch2_btree_pos_to_text.

changes in v2:
- make commit message more verbose.
- set topology error, print error message and return
appropriate error code.

link to v1: https://lore.kernel.org/linux-bcachefs/20241023072024.98915-3-pZ010001011111@xxxxxxxxx/
link to v2: https://lore.kernel.org/linux-bcachefs/20241026174155.233430-3-pZ010001011111@xxxxxxxxx/

fs/bcachefs/btree_iter.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index 15ac72b1af51..acf70aaf2fd2 100644
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -880,6 +880,18 @@ static noinline int btree_node_iter_and_journal_peek(struct btree_trans *trans,
__bch2_btree_and_journal_iter_init_node_iter(trans, &jiter, l->b, l->iter, path->pos);

k = bch2_btree_and_journal_iter_peek(&jiter);
+ if (!k.k) {
+ struct printbuf buf = PRINTBUF;
+
+ prt_str(&buf, "node not found at pos ");
+ bch2_bpos_to_text(&buf, path->pos);
+ prt_str(&buf, " at btree ");
+ bch2_btree_pos_to_text(&buf, c, l->b);
+
+ ret = bch2_fs_topology_error(c, "%s", buf.buf);
+ printbuf_exit(&buf);
+ goto err;
+ }

bch2_bkey_buf_reassemble(out, c, k);

@@ -887,6 +899,7 @@ static noinline int btree_node_iter_and_journal_peek(struct btree_trans *trans,
c->opts.btree_node_prefetch)
ret = btree_path_prefetch_j(trans, path, &jiter);

+err:
bch2_btree_and_journal_iter_exit(&jiter);
return ret;
}
--
2.47.0