Re: [PATCH v3] mmc: mmc_test: Fix __counted_by handling after kzalloc_flex() conversion

[Ulf Hansson]

On Tue, Jun 2, 2026 at 10:13 PM Prabhakar <prabhakar.csengg@xxxxxxxxx> wrote:
>
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
>
> Fix logic issues introduced by the kzalloc_flex() conversion in
> mmc_test_alloc_mem() due to interaction with the __counted_by
> annotation on the flexible array.
>
> Bounds-checking sanitizers rely on the counter field reflecting the
> allocated array size before any array access occurs. However, use
> mem->cnt both as the allocation size and as the runtime insertion
> index, causing incorrect indexing and potentially invalid bounds
> tracking.
>
> Initialize mem->cnt to the maximum allocated number of segments
> immediately after kzalloc_flex(), then use a separate local index
> variable to track successfully allocated entries. Update mem->cnt to
> the actual number of initialized elements before returning or entering
> the cleanup path.
>
> Also rewrite mmc_test_free_mem() to use a forward for-loop, improving
> readability and ensuring only initialized entries are freed.
>
> Fixes: c3126dccfd7b ("mmc: mmc_test: use kzalloc_flex")
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Applied for fixes, thanks!

Kind regards
Uffe


> ---
> v2->v3:
> - Switched back to v1 version of the patch.
> - Addressed review comments from Geert.
> - Add RB tag from Geert which was received on v1.
>
> v1->v2:
> - Started with cnt = 0 and incremented before assignment to ensure
>   accurate tracking of initialized entries in mmc_test_alloc_mem().
> - In mmc_test_free_mem(), replaced the while loop with a forward for-loop to
>   safely iterate over initialized entries without risking underflow.
> - Updated commit message to clarify the issue and the fix.
>
> v2: https://lore.kernel.org/all/20260519133025.618255-1-prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx/
> v1: https://lore.kernel.org/all/20260513201315.3186621-1-prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx/
> ---
>  drivers/mmc/core/mmc_test.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc_test.c b/drivers/mmc/core/mmc_test.c
> index ab38e4c45a8d..4dc16649e61d 100644
> --- a/drivers/mmc/core/mmc_test.c
> +++ b/drivers/mmc/core/mmc_test.c
> @@ -318,9 +318,9 @@ static void mmc_test_free_mem(struct mmc_test_mem *mem)
>  {
>         if (!mem)
>                 return;
> -       while (mem->cnt--)
> -               __free_pages(mem->arr[mem->cnt].page,
> -                            mem->arr[mem->cnt].order);
> +       for (unsigned int i = 0; i < mem->cnt; i++)
> +               __free_pages(mem->arr[i].page,
> +                            mem->arr[i].order);
>         kfree(mem);
>  }
>
> @@ -341,6 +341,7 @@ static struct mmc_test_mem *mmc_test_alloc_mem(unsigned long min_sz,
>         unsigned long page_cnt = 0;
>         unsigned long limit = nr_free_buffer_pages() >> 4;
>         struct mmc_test_mem *mem;
> +       unsigned int idx = 0;
>
>         if (max_page_cnt > limit)
>                 max_page_cnt = limit;
> @@ -375,23 +376,26 @@ static struct mmc_test_mem *mmc_test_alloc_mem(unsigned long min_sz,
>                                 goto out_free;
>                         break;
>                 }
> -               mem->arr[mem->cnt].page = page;
> -               mem->arr[mem->cnt].order = order;
> -               mem->cnt += 1;
> +               mem->arr[idx].page = page;
> +               mem->arr[idx].order = order;
> +               idx += 1;
>                 if (max_page_cnt <= (1UL << order))
>                         break;
>                 max_page_cnt -= 1UL << order;
>                 page_cnt += 1UL << order;
> -               if (mem->cnt >= max_segs) {
> +               if (idx >= mem->cnt) {
>                         if (page_cnt < min_page_cnt)
>                                 goto out_free;
>                         break;
>                 }
>         }
>
> +       mem->cnt = idx;
> +
>         return mem;
>
>  out_free:
> +       mem->cnt = idx;
>         mmc_test_free_mem(mem);
>         return NULL;
>  }
> --
> 2.54.0
>