[PATCH v3 1/2] xfs: avoid LR buffer overrun due to crafted h_{len,size}

[Gao Xiang <hsiangkao@redhat.com>]

Currently, crafted h_len has been blocked for the log
header of the tail block in commit a70f9fe52daa ("xfs:
detect and handle invalid iclog size set by mkfs").

However, each log record could still have crafted h_len,
h_size and cause log record buffer overrun. So let's
check (h_len vs h_size) and (h_size vs buffer size)
for each log record as well instead.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
v2: https://lore.kernel.org/r/20200902141923.26422-1-hsiangkao@redhat.com

changes since v2:
 - rename argument h_size to bufsize to make it clear (Brian);
 - leave the mkfs workaround logic in xlog_do_recovery_pass() (Brian);
 - add XLOG_VERSION_2 checking logic since old logrecv1 doesn't have
   h_size field just to be safe.

 fs/xfs/xfs_log_recover.c | 50 +++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 21 deletions(-)

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index e2ec91b2d0f4..28d952794bfa 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -2904,9 +2904,10 @@ STATIC int
 xlog_valid_rec_header(
 	struct xlog		*log,
 	struct xlog_rec_header	*rhead,
-	xfs_daddr_t		blkno)
+	xfs_daddr_t		blkno,
+	int			bufsize)
 {
-	int			hlen;
+	int			hlen, hsize = XLOG_BIG_RECORD_BSIZE;
 
 	if (XFS_IS_CORRUPT(log->l_mp,
 			   rhead->h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM)))
@@ -2920,10 +2921,22 @@ xlog_valid_rec_header(
 		return -EFSCORRUPTED;
 	}
 
-	/* LR body must have data or it wouldn't have been written */
+	/*
+	 * LR body must have data (or it wouldn't have been written) and
+	 * h_len must not be greater than h_size with one exception (see
+	 * comments in xlog_do_recovery_pass()).
+	 */
 	hlen = be32_to_cpu(rhead->h_len);
-	if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > INT_MAX))
+	if (xfs_sb_version_haslogv2(&log->l_mp->m_sb) &&
+	    (be32_to_cpu(rhead->h_version) & XLOG_VERSION_2))
+		hsize = be32_to_cpu(rhead->h_size);
+
+	if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > hsize))
 		return -EFSCORRUPTED;
+
+	if (bufsize && XFS_IS_CORRUPT(log->l_mp, bufsize < hsize))
+		return -EFSCORRUPTED;
+
 	if (XFS_IS_CORRUPT(log->l_mp,
 			   blkno > log->l_logBBsize || blkno > INT_MAX))
 		return -EFSCORRUPTED;
@@ -2984,9 +2997,6 @@ xlog_do_recovery_pass(
 			goto bread_err1;
 
 		rhead = (xlog_rec_header_t *)offset;
-		error = xlog_valid_rec_header(log, rhead, tail_blk);
-		if (error)
-			goto bread_err1;
 
 		/*
 		 * xfsprogs has a bug where record length is based on lsunit but
@@ -3001,21 +3011,19 @@ xlog_do_recovery_pass(
 		 */
 		h_size = be32_to_cpu(rhead->h_size);
 		h_len = be32_to_cpu(rhead->h_len);
-		if (h_len > h_size) {
-			if (h_len <= log->l_mp->m_logbsize &&
-			    be32_to_cpu(rhead->h_num_logops) == 1) {
-				xfs_warn(log->l_mp,
+		if (h_len > h_size && h_len <= log->l_mp->m_logbsize &&
+		    rhead->h_num_logops == cpu_to_be32(1)) {
+			xfs_warn(log->l_mp,
 		"invalid iclog size (%d bytes), using lsunit (%d bytes)",
-					 h_size, log->l_mp->m_logbsize);
-				h_size = log->l_mp->m_logbsize;
-			} else {
-				XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW,
-						log->l_mp);
-				error = -EFSCORRUPTED;
-				goto bread_err1;
-			}
+				 h_size, log->l_mp->m_logbsize);
+			h_size = log->l_mp->m_logbsize;
+			rhead->h_size = cpu_to_be32(h_size);
 		}
 
+		error = xlog_valid_rec_header(log, rhead, tail_blk, 0);
+		if (error)
+			goto bread_err1;
+
 		if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) &&
 		    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
 			hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
@@ -3096,7 +3104,7 @@ xlog_do_recovery_pass(
 			}
 			rhead = (xlog_rec_header_t *)offset;
 			error = xlog_valid_rec_header(log, rhead,
-						split_hblks ? blk_no : 0);
+					split_hblks ? blk_no : 0, h_size);
 			if (error)
 				goto bread_err2;
 
@@ -3177,7 +3185,7 @@ xlog_do_recovery_pass(
 			goto bread_err2;
 
 		rhead = (xlog_rec_header_t *)offset;
-		error = xlog_valid_rec_header(log, rhead, blk_no);
+		error = xlog_valid_rec_header(log, rhead, blk_no, h_size);
 		if (error)
 			goto bread_err2;
 
-- 
2.18.1