linux-kernel - Re: [PATCH] drm/amdkfd: fix potential null pointer dereference on pointer peer

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Date:   Tue, 2 Jul 2019 15:29:27 +0000
From:   "Liu, Shaoyun" <Shaoyun.Liu@....com>
To:     Colin King <colin.king@...onical.com>,
        Oded Gabbay <oded.gabbay@...il.com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Zhou, David(ChunMing)" <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>
CC:     "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amdkfd: fix potential null pointer dereference on
 pointer peer_dev

 From the comments , "we will  loop GPUs that already be processed (with 
lower value of proximity_domain) ",  the device should already been 
added into the  topology_device_list.  So in this case , 
kfd_topology_device_by_proximity_domain will not return a NULL pointer.  
If you really get the null pointer dereferences here , we must have  
some bigger problem and  can not solved by added the null check here.

Regards

shaoyun.liu

On 2019-06-29 9:31 a.m., Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
>
> The call to kfd_topology_device_by_proximity_domain can return a NULL
> pointer so add a null pointer check on peer_dev to the existing null
> pointer check on peer_dev->gpu to avoid any potential null pointer
> dereferences.
>
> Addresses-Coverity: ("Dereference on null return value")
> Fixes: ae9a25aea7f3 ("drm/amdkfd: Generate xGMI direct iolink")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_crat.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_crat.c b/drivers/gpu/drm/amd/amdkfd/kfd_crat.c
> index 4e3fc284f6ac..cb6b46cfa6c2 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_crat.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_crat.c
> @@ -1293,7 +1293,7 @@ static int kfd_create_vcrat_image_gpu(void *pcrat_image,
>   	if (kdev->hive_id) {
>   		for (nid = 0; nid < proximity_domain; ++nid) {
>   			peer_dev = kfd_topology_device_by_proximity_domain(nid);
> -			if (!peer_dev->gpu)
> +			if (!peer_dev || !peer_dev->gpu)
>   				continue;
>   			if (peer_dev->gpu->hive_id != kdev->hive_id)
>   				continue;