[PATCH 2/3] metadump: bounds check btree block regions being zeroed

[Dave Chinner]

From: Dave Chinner <dchinner at redhat.com>

Arkadiusz Miskiewicz reported that metadump was crashing on one of
his corrupted filesystems, and the trace indicated that it was
zeroing unused regions in inode btree blocks when it failed. The
btree block had a corrupt nrecs field, which was resulting in an out
of bounds memset() occurring.  Ensure that the region being
generated for zeroing is within bounds before executing the zeroing.

Reported-by: Arkadiusz Miskiewicz <arekm at maven.pl>
Signed-off-by: Dave Chinner <dchinner at redhat.com>
---
 db/metadump.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/db/metadump.c b/db/metadump.c
index a185da5..26a3bd5 100644
--- a/db/metadump.c
+++ b/db/metadump.c
@@ -246,6 +246,11 @@ write_buf(
 	return seenint() ? -EINTR : 0;
 }
 
+/*
+ * We could be processing a corrupt block, so we can't trust any of
+ * the offsets or lengths to be within the buffer range. Hence check
+ * carefully!
+ */
 static void
 zero_btree_node(
 	struct xfs_btree_block	*block,
@@ -262,10 +267,15 @@ zero_btree_node(
 	char			*key_end;
 
 	nrecs = be16_to_cpu(block->bb_numrecs);
+	if (nrecs < 0)
+		return;
 
 	switch (btype) {
 	case TYP_BMAPBTA:
 	case TYP_BMAPBTD:
+		if (nrecs > mp->m_bmap_dmxr[1])
+			return;
+
 		bkp = XFS_BMBT_KEY_ADDR(mp, block, 1);
 		bpp = XFS_BMBT_PTR_ADDR(mp, block, 1, mp->m_bmap_dmxr[1]);
 		zp1 = (char *)&bkp[nrecs];
@@ -274,6 +284,9 @@ zero_btree_node(
 		break;
 	case TYP_INOBT:
 	case TYP_FINOBT:
+		if (nrecs > mp->m_inobt_mxr[1])
+			return;
+
 		ikp = XFS_INOBT_KEY_ADDR(mp, block, 1);
 		ipp = XFS_INOBT_PTR_ADDR(mp, block, 1, mp->m_inobt_mxr[1]);
 		zp1 = (char *)&ikp[nrecs];
@@ -282,6 +295,9 @@ zero_btree_node(
 		break;
 	case TYP_BNOBT:
 	case TYP_CNTBT:
+		if (nrecs > mp->m_alloc_mxr[1])
+			return;
+
 		akp = XFS_ALLOC_KEY_ADDR(mp, block, 1);
 		app = XFS_ALLOC_PTR_ADDR(mp, block, 1, mp->m_alloc_mxr[1]);
 		zp1 = (char *)&akp[nrecs];
@@ -300,6 +316,11 @@ zero_btree_node(
 	memset(zp2, 0, (char *)block + mp->m_sb.sb_blocksize - zp2);
 }
 
+/*
+ * We could be processing a corrupt block, so we can't trust any of
+ * the offsets or lengths to be within the buffer range. Hence check
+ * carefully!
+ */
 static void
 zero_btree_leaf(
 	struct xfs_btree_block	*block,
@@ -312,20 +333,31 @@ zero_btree_leaf(
 	char			*zp;
 
 	nrecs = be16_to_cpu(block->bb_numrecs);
+	if (nrecs < 0)
+		return;
 
 	switch (btype) {
 	case TYP_BMAPBTA:
 	case TYP_BMAPBTD:
+		if (nrecs > mp->m_bmap_dmxr[0])
+			return;
+
 		brp = XFS_BMBT_REC_ADDR(mp, block, 1);
 		zp = (char *)&brp[nrecs];
 		break;
 	case TYP_INOBT:
 	case TYP_FINOBT:
+		if (nrecs > mp->m_inobt_mxr[0])
+			return;
+
 		irp = XFS_INOBT_REC_ADDR(mp, block, 1);
 		zp = (char *)&irp[nrecs];
 		break;
 	case TYP_BNOBT:
 	case TYP_CNTBT:
+		if (nrecs > mp->m_alloc_mxr[0])
+			return;
+
 		arp = XFS_ALLOC_REC_ADDR(mp, block, 1);
 		zp = (char *)&arp[nrecs];
 		break;
-- 
2.5.0