From: Jerry Lee <jerrylee@qnap.com>
Date: Sun, 6 Aug 2017 05:18:31 +0000 (-0400)
Subject: ext4: fix overflow caused by missing cast in ext4_resize_fs()
X-Git-Tag: v4.13-rc4~2^2~1
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=aec51758ce10a9c847a62a48a168f8c804c6e053;p=linux-block.git

ext4: fix overflow caused by missing cast in ext4_resize_fs()

On a 32-bit platform, the value of n_blcoks_count may be wrong during
the file system is resized to size larger than 2^32 blocks.  This may
caused the superblock being corrupted with zero blocks count.

Fixes: 1c6bd7173d66
Signed-off-by: Jerry Lee <jerrylee@qnap.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org # 3.7+
---

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index c3ed9021b781..035cd3f4785e 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1927,7 +1927,8 @@ retry:
 			n_desc_blocks = o_desc_blocks +
 				le16_to_cpu(es->s_reserved_gdt_blocks);
 			n_group = n_desc_blocks * EXT4_DESC_PER_BLOCK(sb);
-			n_blocks_count = n_group * EXT4_BLOCKS_PER_GROUP(sb);
+			n_blocks_count = (ext4_fsblk_t)n_group *
+				EXT4_BLOCKS_PER_GROUP(sb);
 			n_group--; /* set to last group number */
 		}