Re: [PATCH] ntfs: change check order in ntfs_attr_find

["chenxiaosong (A)" <chenxiaosong2@huawei.com>]

在 2022/8/26 20:27, Hawkins Jiawei 写道:
> syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> Looks like it is improper check order that causes this bug.
> 
> Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
> ---
>   fs/ntfs/attrib.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
> index 52615e6090e1..6480cd2d371d 100644
> --- a/fs/ntfs/attrib.c
> +++ b/fs/ntfs/attrib.c
> @@ -594,10 +594,11 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
>   	for (;;	a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
>   		u8 *mrec_end = (u8 *)ctx->mrec +
>   		               le32_to_cpu(ctx->mrec->bytes_allocated);
> +		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end)
> +			break;
>   		u8 *name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
>   			       a->name_length * sizeof(ntfschar);
> -		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
> -		    name_end > mrec_end)
> +		if (name_end > mrec_end)
>   			break;
>   		ctx->attr = a;
>   		if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
> 

The reason is that a->length is 0, it will occur uaf when deref any 
field of ATTR_RECORD.

It seems that changing check order will not fix root cause, if the 
condition "if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end)" is false, 
uaf will still occur.

Do you have any thoughts on this ?