[PATCH] bcachefs: assign return error when iterating through layout

[Diogo Jahchan Koike]

syzbot reported a null ptr deref in __copy_user [0]

In __bch2_read_super, when a corrupt backup superblock matches the
default opts offset, no error is assigned to ret and the freed superblock
gets through, possibly being assigned as the best sb in bch2_fs_open and
being later dereferenced, causing a fault. Assign EINVALID to ret when
iterating through layout.

[0]: https://syzkaller.appspot.com/bug?extid=18a5c5e8a9c856944876

Reported-by: syzbot+18a5c5e8a9c856944876@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=18a5c5e8a9c856944876
Signed-off-by: Diogo Jahchan Koike <djahchankoike@xxxxxxxxx>
---
 fs/bcachefs/super-io.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index c8c2ccbdfbb5..fbca0bd302db 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -796,8 +796,10 @@ static int __bch2_read_super(const char *path, struct bch_opts *opts,
 	     i < layout.sb_offset + layout.nr_superblocks; i++) {
 		offset = le64_to_cpu(*i);
 
-		if (offset == opt_get(*opts, sb))
+		if (offset == opt_get(*opts, sb)) {
+			ret = -BCH_ERR_invalid;
 			continue;
+		}
 
 		ret = read_one_super(sb, offset, &err);
 		if (!ret)
-- 
2.43.0