linux-kernel - [PATCH 3.16 088/366] ext4: fix fencepost error in check for inode count overflow during resize

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Date:   Sun, 11 Nov 2018 19:49:05 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jaco Kroon" <jaco@....co.za>,
        "Andreas Dilger" <adilger@...ger.ca>,
        "Theodore Ts'o" <tytso@....edu>, "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.16 088/366] ext4: fix fencepost error in check for inode
 count overflow during resize

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit 4f2f76f751433908364ccff82f437a57d0e6e9b7 upstream.

ext4_resize_fs() has an off-by-one bug when checking whether growing of
a filesystem will not overflow inode count. As a result it allows a
filesystem with 8192 inodes per group to grow to 64TB which overflows
inode count to 0 and makes filesystem unusable. Fix it.

Fixes: 3f8a6411fbada1fa482276591e037f3b1adcf55b
Reported-by: Jaco Kroon <jaco@....co.za>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Reviewed-by: Andreas Dilger <adilger@...ger.ca>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/resize.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1906,7 +1906,7 @@ retry:
 		return 0;
 
 	n_group = ext4_get_group_number(sb, n_blocks_count - 1);
-	if (n_group > (0xFFFFFFFFUL / EXT4_INODES_PER_GROUP(sb))) {
+	if (n_group >= (0xFFFFFFFFUL / EXT4_INODES_PER_GROUP(sb))) {
 		ext4_warning(sb, "resize would cause inodes_count overflow");
 		return -EINVAL;
 	}