Re: [PATCH] mtd: intel-dg: fix array-index-out-of-bounds in intel_dg_mtd_probe()

Randy Dunlap
2025-12-20T07:06:06Z

Hi,

On 12/19/25 10:41 PM, Gustavo A. R. Silva wrote:
> Fix the UBSAN: array-index-out-of-bounds issue below by updating
> counter nvm->nregions before the first access to flexible-array
> member nvm->regions[].

Yeah, I suspected something like that but didn't find any in-tree
documentation about it.

> from kernel bugzilla:
> https://bugzilla.kernel.org/show_bug.cgi?id=220823
>
> Dec 15 22:01:52 orpheus kernel: UBSAN: array-index-out-of-bounds in /var/tmp/portage/sys-kernel/gentoo-kernel-6.18.1/work/linux-6.18/drivers/mtd/devices/mtd_intel_dg.c:750:15
>
> Notice that this flexible array is annotated with the counted_by()
> attribute, hence the counter must always be updated before the
> first access to the array.
>
> Cc: stable@vger.kernel.org
> Fixes: ceb5ab3cb646 ("mtd: add driver for intel graphics non-volatile memory device")
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Closes: https://lore.kernel.org/linux-hardening/90e419ad-4036-4669-a4cc-8ce5d29e464b@infradead.org/

More appropriately:
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220823

Acked-by: Randy Dunlap <rdunlap@infradead.org>

Thanks.

> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> drivers/mtd/devices/mtd_intel_dg.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/mtd/devices/mtd_intel_dg.c b/drivers/mtd/devices/mtd_intel_dg.c
> index 2bab30dcd35f..d3e89fe324b8 100644
> --- a/drivers/mtd/devices/mtd_intel_dg.c
> +++ b/drivers/mtd/devices/mtd_intel_dg.c
> @@ -768,6 +768,9 @@ static int intel_dg_mtd_probe(struct auxiliary_device *aux_dev,
> if (!nvm)
> return -ENOMEM;
>
> + /* Update nvm->nregions before first access to nvm->regions[] below. */
> + nvm->nregions = nregions;
> +
> kref_init(&nvm->refcnt);
> mutex_init(&nvm->lock);
>

--
~Randy