Am 25.10.24 um 11:05 schrieb Tvrtko Ursulin:

On 25/10/2024 09:59, Tvrtko Ursulin wrote:

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On 24/10/2024 13:41, Christian König wrote:

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Reports indicates that some userspace applications try to merge more than 80k of fences into a single dma_fence_array leading to a warning from kzalloc() that the requested size becomes to big.

While that is clearly an userspace bug we should probably handle that case gracefully in the kernel.

So we can either reject requests to merge more than a reasonable amount of fences (64k maybe?) or we can start to use kvzalloc() instead of kzalloc(). This patch here does the later.

Rejecting would potentially be safer, otherwise there is a path for userspace to trigger a warn in kvmalloc_node (see 0829b5bcdd3b ("drm/i915: 2 GiB of relocations ought to be enough for anybody*")) and spam dmesg at will.

Actually that is a WARN_ON_*ONCE* there so maybe not so critical to invent a limit. Up for discussion I suppose.

Regards,

Tvrtko

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Question is what limit to set...

That's one of the reasons why I opted for kvzalloc() initially.

I mean we could use some nice round number like 65536, but that would be totally arbitrary.

Any comments on the other two patches? I need to get them upstream.

Thanks, Christian.

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Regards,

Tvrtko

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Signed-off-by: Christian König christian.koenig@amd.com CC: stable@vger.kernel.org

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drivers/dma-buf/dma-fence-array.c | 6 +++---   1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c index 8a08ffde31e7..46ac42bcfac0 100644 --- a/drivers/dma-buf/dma-fence-array.c +++ b/drivers/dma-buf/dma-fence-array.c @@ -119,8 +119,8 @@ static void dma_fence_array_release(struct dma_fence *fence)       for (i = 0; i < array->num_fences; ++i)           dma_fence_put(array->fences[i]); -    kfree(array->fences); -    dma_fence_free(fence); +    kvfree(array->fences); +    kvfree_rcu(fence, rcu);   }   static void dma_fence_array_set_deadline(struct dma_fence *fence, @@ -153,7 +153,7 @@ struct dma_fence_array *dma_fence_array_alloc(int num_fences)   {       struct dma_fence_array *array; -    return kzalloc(struct_size(array, callbacks, num_fences), GFP_KERNEL); +    return kvzalloc(struct_size(array, callbacks, num_fences), GFP_KERNEL);   }   EXPORT_SYMBOL(dma_fence_array_alloc);