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

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Message-ID: <bmdour3gw4tuwqgvvw764p4ot3nnltqm4e7n3edlbtpfazvp5c@cqe5dwgc66uy>
Date: Tue, 8 Apr 2025 12:39:56 +0300
From: Fedor Pchelkin <pchelkin@...ras.ru>
To: Christian König <christian.koenig@....com>
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

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.