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

[Lad, Prabhakar]

Hi Geert,

On Tue, May 19, 2026 at 11:09 AM Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Prabhakar,
>
> On Tue, 19 May 2026 at 12:05, Lad, Prabhakar <prabhakar.csengg@xxxxxxxxx> wrote:
> > On Mon, May 18, 2026 at 12:08 PM Geert Uytterhoeven
> > <geert@xxxxxxxxxxxxxx> wrote:
> > > On Wed, 13 May 2026 at 22:13, 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>
>
> > > > --- a/drivers/mmc/core/mmc_test.c
> > > > +++ b/drivers/mmc/core/mmc_test.c
> > > > @@ -316,11 +316,13 @@ static int mmc_test_buffer_transfer(struct mmc_test_card *test,
> > > >
> > > >  static void mmc_test_free_mem(struct mmc_test_mem *mem)
> > > >  {
> > > > +       unsigned int idx;
> > > > +
> > > >         if (!mem)
> > > >                 return;
> > > > -       while (mem->cnt--)
> > > > -               __free_pages(mem->arr[mem->cnt].page,
> > > > -                            mem->arr[mem->cnt].order);
> > > > +       for (idx = 0; idx < mem->cnt; idx++)
> > >
> > > for (unsigned int i; ...)?
> > >
> > Ok.
> >
> > > > +               __free_pages(mem->arr[idx].page,
> > > > +                            mem->arr[idx].order);
> > > >         kfree(mem);
> > > >  }
> > > >
> > > > @@ -341,6 +343,7 @@ 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;
> > > > @@ -356,6 +359,7 @@ static struct mmc_test_mem *mmc_test_alloc_mem(unsigned long min_sz,
> > > >         mem = kzalloc_flex(*mem, arr, max_segs);
> > > >         if (!mem)
> > > >                 return NULL;
> > > > +       mem->cnt = max_segs;
> > > >
> > > >         while (max_page_cnt) {
> > > >                 struct page *page;
> > > > @@ -375,23 +379,26 @@ 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;
> > >
> > > While looking rather ugly, I think starting with mem->cnt at zero,
> > > and updating it in each step like
> > >
> > >     mem->cnt++;
> > >     mem->arr[mem->cnt - 1].page = page;
> > >     mem->arr[mem->cnt - 1].order = order;
> > >
> > > would still be better, as it makes the dependency between mem->cnt and
> > > the size of mem->arr[] clearer (located closer to each other), and ...
> > >
> > >
> > Ok, I will start with mem->cnt at zero; with this I can drop changes
> > in mmc_test_free_mem().
>
> I don't think you can drop these changes, as mmc_test_free_mem()
> does mem->cnt-- _before_ accessing mem->arr[mem->cnt].
>
Ack.

Cheers,
Prabhakar