[PATCH] xfs: validate buffer log item before reordering

[Weiming Shi <bestswngs@gmail.com>]

Log recovery reorders transaction items before buffer item pass1 validates
the format of region 0.  A corrupt log can therefore supply a four-byte
region containing only blf_type and blf_size.  xlog_recover_buf_reorder()
then reads blf_flags immediately past the allocation:

  BUG: KASAN: slab-out-of-bounds in xlog_recover_buf_reorder
  Read of size 2 at addr ffff88800e40e364 by task poc/133
  Call Trace:
   kasan_report mm/kasan/report.c:595
   xlog_recover_buf_reorder fs/xfs/xfs_buf_item_recover.c:164
   xlog_recover_reorder_trans fs/xfs/xfs_log_recover.c:1929
   xlog_recover_commit_trans fs/xfs/xfs_log_recover.c:2053
   xlog_recovery_process_trans fs/xfs/xfs_log_recover.c:2319
   xlog_recover_process_data fs/xfs/xfs_log_recover.c:2510
   xlog_do_recovery_pass fs/xfs/xfs_log_recover.c:3253
   xlog_do_log_recovery fs/xfs/xfs_log_recover.c:3340
   xlog_do_recover fs/xfs/xfs_log_recover.c:3377
   xlog_recover fs/xfs/xfs_log_recover.c:3502
   xfs_log_mount fs/xfs/xfs_log.c:617
   xfs_mountfs fs/xfs/xfs_mount.c:1031
  The buggy address is located 0 bytes to the right of
  allocated 4-byte region [ffff88800e40e360, ffff88800e40e364)

Validate region 0 before inspecting the flags.  Keep a malformed item on
the regular item list so that xlog_recover_buf_commit_pass1() reports the
corrupt log through the existing error path.

Fixes: 86ffa471d9ce ("xfs: refactor log recovery item sorting into a generic dispatch structure")
Reported-by: co+af981e62f5c7171a@bugs.sh
Closes: https://lore.kernel.org/all/aqZALi7GdVprcNOh@cronus.toxiclabs.cc/
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 fs/xfs/xfs_buf_item_recover.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/xfs/xfs_buf_item_recover.c b/fs/xfs/xfs_buf_item_recover.c
index 57929f115055..70e69ec731ac 100644
--- a/fs/xfs/xfs_buf_item_recover.c
+++ b/fs/xfs/xfs_buf_item_recover.c
@@ -161,6 +161,10 @@ xlog_recover_buf_reorder(
 {
 	struct xfs_buf_log_format	*buf_f = item->ri_buf[0].iov_base;
 
+	/* A short region 0 is rejected by xlog_recover_buf_commit_pass1. */
+	if (!xfs_buf_log_check_iovec(&item->ri_buf[0]))
+		return XLOG_REORDER_ITEM_LIST;
+
 	if (buf_f->blf_flags & XFS_BLF_CANCEL)
 		return XLOG_REORDER_CANCEL_LIST;
 	if (buf_f->blf_flags & XFS_BLF_INODE_BUF)
-- 
2.55.0