[PATCH 2/2] repair: check ino alignment value to avoid mod by zero

[Brian Foster]

xfs_repair checks inode records for valid alignment according to the
alignment specified in the superblock. It currently performs the
alignment check whenever fs_aligned_inodes is set, which is determined
based on whether the fs supports the field.

Support for the field does not guarantee its value is non-zero, however.
For example, a large block size fs on a large page size arch (e.g.,
ppc64):

	mkfs.xfs -f -m crc=1,finobt=1 -b size=64k <dev>

... can lead to incorrect badly aligned inode record messages from
xfs_repair and other problems.

Update the inobt and finobt checks to verify that alignment is a
non-zero value before attempting to use it to divide (mod) by zero.

Signed-off-by: Brian Foster <bfoster at redhat.com>
---
 repair/scan.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/repair/scan.c b/repair/scan.c
index 142d8d7..ce8d7f5 100644
--- a/repair/scan.c
+++ b/repair/scan.c
@@ -770,7 +770,8 @@ scan_single_ino_chunk(
 	    (inodes_per_block <= XFS_INODES_PER_CHUNK && off !=  0) ||
 	    (inodes_per_block > XFS_INODES_PER_CHUNK &&
 	     off % XFS_INODES_PER_CHUNK != 0) ||
-	    (fs_aligned_inodes && agbno % fs_ino_alignment != 0))  {
+	    (fs_aligned_inodes && fs_ino_alignment &&
+	     agbno % fs_ino_alignment != 0))  {
 		do_warn(
 	_("badly aligned inode rec (starting inode = %" PRIu64 ")\n"),
 			lino);
@@ -929,7 +930,8 @@ scan_single_finobt_chunk(
 	    (inodes_per_block <= XFS_INODES_PER_CHUNK && off !=  0) ||
 	    (inodes_per_block > XFS_INODES_PER_CHUNK &&
 	     off % XFS_INODES_PER_CHUNK != 0) ||
-	    (fs_aligned_inodes && agbno % fs_ino_alignment != 0)) {
+	    (fs_aligned_inodes && fs_ino_alignment &&
+	     agbno % fs_ino_alignment != 0)) {
 		do_warn(
 	_("badly aligned finobt inode rec (starting inode = %" PRIu64 ")\n"),
 			lino);
-- 
1.8.3.1