linux-kernel - Re: [PATCH] mtd: intel-dg: fix array-index-out-of-bounds in intel_dg_mtd

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Message-ID: <4cf65ead-b236-4973-b81b-a45128959a65@infradead.org>
Date: Fri, 19 Dec 2025 23:05:58 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Alexander Usyskin <alexander.usyskin@...el.com>,
 Miquel Raynal <miquel.raynal@...tlin.com>,
 Richard Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Raag Jadav <raag.jadav@...el.com>,
 Tomas Winkler <tomasw@...il.com>
Cc: linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] mtd: intel-dg: fix array-index-out-of-bounds in
 intel_dg_mtd_probe()

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@...r.kernel.org
> Fixes: ceb5ab3cb646 ("mtd: add driver for intel graphics non-volatile memory device")
> Reported-by: Randy Dunlap <rdunlap@...radead.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@...radead.org>

Thanks.

> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.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