ext4: fix potential integer overflow in alloc_flex_gd()

In alloc_flex_gd(), when flexbg_size is large, kmalloc size would
overflow and flex_gd->groups would point to a buffer smaller than
expected, causing OOB accesses when it is used.

Note that in ext4_resize_fs(), flexbg_size is calculated using
sbi->s_log_groups_per_flex, which is read from the disk and only bounded
to [1, 31]. The patch returns NULL for too large flexbg_size.

Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Haogang Chen <haogangchen@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index a58ce7c507ae..05c7979226e5 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -161,6 +161,8 @@ static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned long flexbg_size)
         if (flex_gd == NULL)
                 goto out3;
 
+        if (flexbg_size >= UINT_MAX / sizeof(struct ext4_new_flex_group_data))
+                goto out2;
         flex_gd->count = flexbg_size;
 
         flex_gd->groups = kmalloc(sizeof(struct ext4_new_group_data) *