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

[Raag Jadav]

On Sat, Dec 20, 2025 at 03:41:49PM +0900, 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[].
> 
> 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.

Already fixed[1], but not sure if it's landed yet.

[1] https://lore.kernel.org/linux-mtd/20251111-mtd-nregions-v1-1-61db61e78c63@xxxxxxxxx/

Raag

> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: ceb5ab3cb646 ("mtd: add driver for intel graphics non-volatile memory device")
> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-hardening/90e419ad-4036-4669-a4cc-8ce5d29e464b@xxxxxxxxxxxxx/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
>  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);
>  
> -- 
> 2.43.0
>