[PATCH v4] 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 has been
corrupted and therefore we abort processing with a -EFSCORRUPTED error
immediately.

Also, refactor the structure of the validity checks for better
readability. At the default error level (LOW), XFS_IS_CORRUPT() emits
the condition that failed, the file and line number it is
located at, then dumps the stack. This gives us everything we need
to know about the failure if we do a single validity check per
XFS_IS_CORRUPT().

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
v3 -> v4: 
- refactor for readability

 fs/xfs/xfs_log_recover.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index e6ed9e09c027..f5f28755b2ff 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2950,31 +2950,40 @@ xlog_valid_rec_header(
 	xfs_daddr_t		blkno,
 	int			bufsize)
 {
+	struct xfs_mount	*mp = log->l_mp;
+	u32			h_version = be32_to_cpu(rhead->h_version);
 	int			hlen;
 
-	if (XFS_IS_CORRUPT(log->l_mp,
+	if (XFS_IS_CORRUPT(mp,
 			   rhead->h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM)))
 		return -EFSCORRUPTED;
-	if (XFS_IS_CORRUPT(log->l_mp,
-			   (!rhead->h_version ||
-			   (be32_to_cpu(rhead->h_version) &
-			    (~XLOG_VERSION_OKBITS))))) {
-		xfs_warn(log->l_mp, "%s: unrecognised log version (%d).",
-			__func__, be32_to_cpu(rhead->h_version));
+
+	if (XFS_IS_CORRUPT(mp, !h_version))
 		return -EFSCORRUPTED;
-	}
+	if (XFS_IS_CORRUPT(mp, (h_version & ~XLOG_VERSION_OKBITS)))
+		return -EFSCORRUPTED;
+
+	/*
+	 * the log version is known, but must match the superblock log
+	 * version feature bits for the header to be considered valid
+	 */
+	if (xfs_has_logv2(mp)) {
+		if (XFS_IS_CORRUPT(mp, !(h_version & XLOG_VERSION_2)))
+			return -EFSCORRUPTED;
+	} else if (XFS_IS_CORRUPT(mp, !(h_version & XLOG_VERSION_1)))
+			return -EFSCORRUPTED;
 
 	/*
 	 * LR body must have data (or it wouldn't have been written)
 	 * and h_len must not be greater than LR buffer size.
 	 */
 	hlen = be32_to_cpu(rhead->h_len);
-	if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > bufsize))
+	if (XFS_IS_CORRUPT(mp, hlen <= 0 || hlen > bufsize))
 		return -EFSCORRUPTED;
 
-	if (XFS_IS_CORRUPT(log->l_mp,
-			   blkno > log->l_logBBsize || blkno > INT_MAX))
+	if (XFS_IS_CORRUPT(mp, blkno > log->l_logBBsize || blkno > INT_MAX))
 		return -EFSCORRUPTED;
+
 	return 0;
 }
 
-- 
2.43.0