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SubjectRe: [PATCH] ntfs: change check order in ntfs_attr_find
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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 ?

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