Re: [PATCH v3] Fix null-ptr-deref in bio_integrity_map_user()

[Sungwoo Kim]

This is a follow-up based on Sashiko's comments.
https://sashiko.dev/#/patchset/20260420020327.1667156-3-iam%40sung-woo.kim

On Sun, Apr 19, 2026 at 10:05 PM Sungwoo Kim <iam@xxxxxxxxxxxx> wrote:
>

[snip]

> diff --git a/block/bio-integrity.c b/block/bio-integrity.c
> index e79eaf047794..c8cfd15fb589 100644
> --- a/block/bio-integrity.c
> +++ b/block/bio-integrity.c
> @@ -402,6 +402,20 @@ int bio_integrity_map_user(struct bio *bio, struct iov_iter *iter)
>                                         extraction_flags, &offset);
>         if (unlikely(ret < 0))
>                 goto free_bvec;

It's pre-existing, though, free_bvec does not kvfree(pages), leading
to a memory leak.

> +       /* Handle partial pinning. This can happen when pin_user_pages_fast()
> +        * returns fewer pages than requested
> +        */
> +       if (unlikely(ret != bytes)) {
> +               int npinned = DIV_ROUND_UP(offset + ret, PAGE_SIZE);

If ret == 0, npinned becomes 1, whereas there is no actually pinned memory

> +               int i;
> +
> +               for (i = 0; i < npinned; i++)
> +                       unpin_user_page(pages[i]);

... which results in invalid access here.

Also, pages[i] can be ITER_KVEC, ITER_BVEC, ITER_FOLIOQ, etc., which
do not pin memory.
Thus, calling unpin_user_page(pages[i]) unconditionally is incorrect.

To fix this, call unpin_user_page() when user_backed_iter(iter) is true.

> +               if (pages != stack_pages)
> +                       kvfree(pages);
> +               ret = -EFAULT;
> +               goto free_bvec;
> +       }
>
>         nr_bvecs = bvec_from_pages(bvec, pages, nr_vecs, bytes, offset,
>                                    &is_p2p);
> --
> 2.47.3
>