bcachefs: Fix NULL ptr dereference in btree_node_iter_and_journal_peek

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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=005ef9aa519f30d97657
Fixes: 5222a4607cd8 ("bcachefs: BTREE_ITER_WITH_JOURNAL")
Suggested-by: Alan Huang <mmpgouride@gmail.com>
Suggested-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Piotr Zalewski <pZ010001011111@proton.me>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index 0883cf6e1a3ebcfef787aad618df83a9ba81f2f7..eef9b89c561ddfdd2ef4b886fde90fb012e8e45f 100644 (file)
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -882,6 +882,18 @@ 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);
 
@@ -889,6 +901,7 @@ 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;
 }