linux-ext4 - [PATCH] ext4: fix incorrect n_blocks_count result when resizing file system to size larger than 2^32 blocks

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Date:   Fri, 28 Jul 2017 14:23:55 +0800
From:   Jerry Lee <jerrylee@...p.com>
To:     linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH] ext4: fix incorrect n_blocks_count result when resizing file
 system to size larger than 2^32 blocks

On 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.

Signed-off-by: Jerry Lee <jerrylee@...p.com>
---
 fs/ext4/resize.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index c3ed902..035cd3f 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1927,7 +1927,8 @@ int ext4_resize_fs(struct super_block *sb,
ext4_fsblk_t n_blocks_count)
                        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 */
                }