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    Subject[PATCH] FS: ext4: fix integer overflow in alloc_flex_gd()
    Date
    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.

    Signed-off-by: Haogang Chen <haogangchen@gmail.com>
    ---
    fs/ext4/resize.c | 2 ++
    1 files changed, 2 insertions(+), 0 deletions(-)

    diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
    index f9d948f..8601f4b 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) *
    --
    1.7.5.4


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