xfs: fix overflow in xfs_attr3_leaf_verify

Dave Chinner · djwong · commit 837514f7a4ca · 2018-11-06T07:50:50.000-08:00
generic/070 on 64k block size filesystems is failing with a verifier corruption on writeback or an attribute leaf block: [ 94.973083] XFS (pmem0): Metadata corruption detected at xfs_attr3_leaf_verify+0x246/0x260, xfs_attr3_leaf block 0x811480 [ 94.975623] XFS (pmem0): Unmount and run xfs_repair [ 94.976720] XFS (pmem0): First 128 bytes of corrupted metadata buffer: [ 94.978270] 000000004b2e7b45: 00 00 00 00 00 00 00 00 3b ee 00 00 00 00 00 00 ........;....... [ 94.980268] 000000006b1db90b: 00 00 00 00 00 81 14 80 00 00 00 00 00 00 00 00 ................ [ 94.982251] 00000000433f2407: 22 7b 5c 82 2d 5c 47 4c bb 31 1c 37 fa a9 ce d6 "{\.-\GL.1.7.... [ 94.984157] 0000000010dc7dfb: 00 00 00 00 00 81 04 8a 00 0a 18 e8 dd 94 01 00 ................ [ 94.986215] 00000000d5a19229: 00 a0 dc f4 fe 98 01 68 f0 d8 07 e0 00 00 00 00 .......h........ [ 94.988171] 00000000521df36c: 0c 2d 32 e2 fe 20 01 00 0c 2d 58 65 fe 0c 01 00 .-2.. ...-Xe.... [ 94.990162] 000000008477ae06: 0c 2d 5b 66 fe 8c 01 00 0c 2d 71 35 fe 7c 01 00 .-[f.....-q5.|.. [ 94.992139] 00000000a4a6bca6: 0c 2d 72 37 fc d4 01 00 0c 2d d8 b8 f0 90 01 00 .-r7.....-...... [ 94.994789] XFS (pmem0): xfs_do_force_shutdown(0x8) called from line 1453 of file fs/xfs/xfs_buf.c. Return address = ffffffff815365f3 This is failing this check: end = ichdr.freemap[i].base + ichdr.freemap[i].size; if (end < ichdr.freemap[i].base) >>>>> return __this_address; if (end > mp->m_attr_geo->blksize) return __this_address; And from the buffer output above, the freemap array is: freemap[0].base = 0x00a0 freemap[0].size = 0xdcf4 end = 0xdd94 freemap[1].base = 0xfe98 freemap[1].size = 0x0168 end = 0x10000 freemap[2].base = 0xf0d8 freemap[2].size = 0x07e0 end = 0xf8b8 These all look valid - the block size is 0x10000 and so from the last check in the above verifier fragment we know that the end of freemap[1] is valid. The problem is that end is declared as: uint16_t end; And (uint16_t)0x10000 = 0. So we have a verifier bug here, not a corruption. Fix the verifier to use uint32_t types for the check and hence avoid the overflow. Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=201577 Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
@@ -243,7 +243,7 @@ xfs_attr3_leaf_verify(
 	struct xfs_mount		*mp = bp->b_target->bt_mount;
 	struct xfs_attr_leafblock	*leaf = bp->b_addr;
 	struct xfs_attr_leaf_entry	*entries;
-	uint16_t			end;
+	uint32_t			end;	/* must be 32bit - see below */
 	int				i;
 
 	xfs_attr3_leaf_hdr_from_disk(mp->m_attr_geo, &ichdr, leaf);
@@ -293,6 +293,11 @@ xfs_attr3_leaf_verify(
 	/*
 	 * Quickly check the freemap information.  Attribute data has to be
 	 * aligned to 4-byte boundaries, and likewise for the free space.
+	 *
+	 * Note that for 64k block size filesystems, the freemap entries cannot
+	 * overflow as they are only be16 fields. However, when checking end
+	 * pointer of the freemap, we have to be careful to detect overflows and
+	 * so use uint32_t for those checks.
 	 */
 	for (i = 0; i < XFS_ATTR_LEAF_MAPSIZE; i++) {
 		if (ichdr.freemap[i].base > mp->m_attr_geo->blksize)
@@ -303,7 +308,9 @@ xfs_attr3_leaf_verify(
 			return __this_address;
 		if (ichdr.freemap[i].size & 0x3)
 			return __this_address;
-		end = ichdr.freemap[i].base + ichdr.freemap[i].size;
+
+		/* be care of 16 bit overflows here */
+		end = (uint32_t)ichdr.freemap[i].base + ichdr.freemap[i].size;
 		if (end < ichdr.freemap[i].base)
 			return __this_address;
 		if (end > mp->m_attr_geo->blksize)
