Re: [PATCH] nouveau/dmem: handle kcalloc() allocation failure

[Danilo Krummrich]

Hi Duoming,

On 3/3/24 08:53, Duoming Zhou wrote:
> The kcalloc() in nouveau_dmem_evict_chunk() will return null if
> the physical memory has run out. As a result, if we dereference
> src_pfns, dst_pfns or dma_addrs, the null pointer dereference bugs
> will happen.
>
> This patch uses stack variables to replace the kcalloc().
>
> Fixes: 249881232e14 ("nouveau/dmem: evict device private memory during release")
> Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> ---
>   drivers/gpu/drm/nouveau/nouveau_dmem.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 12feecf71e7..9a578262c6d 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -374,13 +374,13 @@ static void
>   nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
>   {
>   	unsigned long i, npages = range_len(&chunk->pagemap.range) >> PAGE_SHIFT;
> -	unsigned long *src_pfns, *dst_pfns;
> -	dma_addr_t *dma_addrs;
> +	unsigned long src_pfns[npages], dst_pfns[npages];
> +	dma_addr_t dma_addrs[npages];

Please don't use variable length arrays, this can potentially blow up
the stack.

As a fix I think we should allocate with __GFP_NOFAIL instead.

- Danilo

>   	struct nouveau_fence *fence;
>   
> -	src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL);
> -	dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL);
> -	dma_addrs = kcalloc(npages, sizeof(*dma_addrs), GFP_KERNEL);
> +	memset(src_pfns, 0, npages);
> +	memset(dst_pfns, 0, npages);
> +	memset(dma_addrs, 0, npages);
>   
>   	migrate_device_range(src_pfns, chunk->pagemap.range.start >> PAGE_SHIFT,
>   			npages);
> @@ -406,11 +406,8 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
>   	migrate_device_pages(src_pfns, dst_pfns, npages);
>   	nouveau_dmem_fence_done(&fence);
>   	migrate_device_finalize(src_pfns, dst_pfns, npages);
> -	kfree(src_pfns);
> -	kfree(dst_pfns);
>   	for (i = 0; i < npages; i++)
>   		dma_unmap_page(chunk->drm->dev->dev, dma_addrs[i], PAGE_SIZE, DMA_BIDIRECTIONAL);
> -	kfree(dma_addrs);
>   }
>   
>   void