[PATCH] xfs: initialize first bad log block in head verification

[Yousef Alhouseen <alhouseenyousef@gmail.com>]

xlog_do_recovery_pass() only writes first_bad when it reaches the common
error exit after processing a log record. An earlier CRC or corruption
failure can therefore return without initializing the out-parameter.

xlog_verify_head() tests first_bad on those errors and may then use its
uninitialized stack value as a log block number while searching for the
last good record. Initialize it to zero, matching xlog_verify_tail(), so
an error without a recorded bad block is returned directly.

Fixes: 7088c4136fa1 ("xfs: detect and trim torn writes during log recovery")
Reported-by: syzbot+b7dfbed0c6c2b5e9fd34@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b7dfbed0c6c2b5e9fd34
Cc: stable@vger.kernel.org
Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
---
 fs/xfs/xfs_log_recover.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 09e6678ca487..d8125f3add4b 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -1028,7 +1028,7 @@ xlog_verify_head(
 {
 	struct xlog_rec_header	*tmp_rhead;
 	char			*tmp_buffer;
-	xfs_daddr_t		first_bad;
+	xfs_daddr_t		first_bad = 0;
 	xfs_daddr_t		tmp_rhead_blk;
 	int			found;
 	int			error;
-- 
2.54.0