linux-kernel - Re: [lvc-project] [PATCH] drm/amdgpu: check a user-provided number of BOs in list

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Message-ID: <f8810b13-01d1-4615-b6e2-2e791c48b466@amd.com>
Date: Tue, 8 Apr 2025 13:37:17 +0200
From: Christian König <christian.koenig@....com>
To: Fedor Pchelkin <pchelkin@...ras.ru>
Cc: Denis Arefev <arefev@...mel.ru>, Alex Deucher
 <alexander.deucher@....com>, Simona Vetter <simona@...ll.ch>,
 Andrey Grodzovsky <andrey.grodzovsky@....com>, lvc-project@...uxtesting.org,
 Chunming Zhou <david1.zhou@....com>, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
 stable@...r.kernel.org, David Airlie <airlied@...il.com>
Subject: Re: [lvc-project] [PATCH] drm/amdgpu: check a user-provided number of
 BOs in list

Am 08.04.25 um 11:39 schrieb Fedor Pchelkin:
> On Tue, 08. Apr 11:26, Christian König wrote:
>> Am 08.04.25 um 11:17 schrieb Denis Arefev:
>>> The user can set any value to the variable ‘bo_number’, via the ioctl
>>> command DRM_IOCTL_AMDGPU_BO_LIST. This will affect the arithmetic
>>> expression ‘in->bo_number * in->bo_info_size’, which is prone to
>>> overflow. Add a valid value check.
>> As far as I can see that is already checked by kvmalloc_array().
>>
>> So adding this additional check manually is completely superfluous.
> Note that in->bo_number is of type 'u32' while kvmalloc_array() checks for
> an overflow in 'size_t', usually 64-bit.
>
> So it looks possible to pass some large 32-bit number, then multiply it by
> (comparatively small) in->bo_info_size and still remain in 64-bit bounds.
>
> And later that would likely result in a WARNING in
>
> void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node)
> {
> ...
> 	/* Don't even allow crazy sizes */
> 	if (unlikely(size > INT_MAX)) {
> 		WARN_ON_ONCE(!(flags & __GFP_NOWARN));
> 		return NULL;
> 	}
>
> But the commit description lacks such details, I admit.

Yeah, so what? I'm perfectly aware that this can result in a warning, but that is just not something worth fixing.

Christian.