[PATCH v3] xfs: validate log record version against superblock log version

[Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>]

Syzbot creates a fuzzed record where xfs_has_logv2() but the
xlog_rec_header h_version != XLOG_VERSION_2. This causes a
KASAN: slab-out-of-bounds read in xlog_do_recovery_pass() ->
xlog_recover_process() -> xlog_cksum().

Fix by adding a check to xlog_valid_rec_header() to abort journal
recovery if the xlog_rec_header h_version does not match the super
block log version.

A file system with a version 2 log will only ever set
XLOG_VERSION_2 in its headers (and v1 will only ever set V_1), so if
there is any mismatch, either the journal or the superblock as been
corrupted and therefore we abort processing with a -EFSCORRUPTED error
immediately.

Reported-by: syzbot+9f6d080dece587cfdd4c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9f6d080dece587cfdd4c
Tested-by: syzbot+9f6d080dece587cfdd4c@syzkaller.appspotmail.com
Fixes: 45cf976008dd ("xfs: fix log recovery buffer allocation for the legacy h_size fixup")
Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@gmail.com>
---
changelog
v1 -> v2: 
- reject the mount for h_size > XLOG_HEADER_CYCLE_SIZE && !XLOG_VERSION_2
v2 -> v3:
- abort journal recovery if the xlog_rec_header h_version does not match 
the super block log version
- heavily modify commit description

 fs/xfs/xfs_log_recover.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index e6ed9e09c027..b9a708673965 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2963,6 +2963,14 @@ xlog_valid_rec_header(
 			__func__, be32_to_cpu(rhead->h_version));
 		return -EFSCORRUPTED;
 	}
+	if (XFS_IS_CORRUPT(log->l_mp, xfs_has_logv2(log->l_mp) !=
+			   !!(be32_to_cpu(rhead->h_version) & XLOG_VERSION_2))) {
+		xfs_warn(log->l_mp,
+"%s: xlog_rec_header h_version (%d) does not match sb log version (%d)",
+			__func__, be32_to_cpu(rhead->h_version),
+			xfs_has_logv2(log->l_mp) ? 2 : 1);
+		return -EFSCORRUPTED;
+	}
 
 	/*
 	 * LR body must have data (or it wouldn't have been written)
-- 
2.43.0