[PATCH][next] dma-buf: Fix NULL pointer dereference in dma_fence_enable_sw_signaling()

[Kees Cook]

On Wed, Oct 11, 2023 at 08:03:43AM -0600, Gustavo A. R. Silva wrote:
> Currently, a NULL pointer dereference will happen in function
> `dma_fence_enable_sw_signaling()` (at line 615), in case `chain`
> is not allocated in `mock_chain()` and this function returns
> `NULL` (at line 86). See below:
> 
> drivers/dma-buf/st-dma-fence-chain.c:
>  86         chain = mock_chain(NULL, f, 1);
>  87         if (!chain)
>  88                 err = -ENOMEM;
>  89
>  90         dma_fence_enable_sw_signaling(chain);

Instead of the larger patch, should line 88 here just do a "return
-ENOMEM" instead?

-Kees

> 
> drivers/dma-buf/dma-fence.c:
>  611 void dma_fence_enable_sw_signaling(struct dma_fence *fence)
>  612 {
>  613         unsigned long flags;
>  614
>  615         spin_lock_irqsave(fence->lock, flags);
> 			       ^^^^^^^^^^^
> 				    |
> 			  NULL pointer reference
> 			  if fence == NULL
> 
>  616         __dma_fence_enable_signaling(fence);
>  617         spin_unlock_irqrestore(fence->lock, flags);
>  618 }
> 
> Fix this by adding a NULL check before dereferencing `fence` in
> `dma_fence_enable_sw_signaling()`. This will prevent any other NULL
> pointer dereference when the `fence` passed as an argument is `NULL`.
> 
> Addresses-Coverity: ("Dereference after null check")
> Fixes: d62c43a953ce ("dma-buf: Enable signaling on fence for selftests")
> Cc: stable at vger.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org>
> ---
>  drivers/dma-buf/dma-fence.c | 9 ++++++++-
>  include/linux/dma-fence.h   | 2 +-
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 8aa8f8cb7071..4d2f13560d0f 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -607,14 +607,21 @@ static bool __dma_fence_enable_signaling(struct dma_fence *fence)
>   * This will request for sw signaling to be enabled, to make the fence
>   * complete as soon as possible. This calls &dma_fence_ops.enable_signaling
>   * internally.
> + *
> + * Returns 0 on success and a negative error value when @fence is NULL.
>   */
> -void dma_fence_enable_sw_signaling(struct dma_fence *fence)
> +int dma_fence_enable_sw_signaling(struct dma_fence *fence)
>  {
>  	unsigned long flags;
>  
> +	if (!fence)
> +		return -EINVAL;
> +
>  	spin_lock_irqsave(fence->lock, flags);
>  	__dma_fence_enable_signaling(fence);
>  	spin_unlock_irqrestore(fence->lock, flags);
> +
> +	return 0;
>  }
>  EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
>  
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index ebe78bd3d121..1e4025e925e6 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -399,7 +399,7 @@ int dma_fence_add_callback(struct dma_fence *fence,
>  			   dma_fence_func_t func);
>  bool dma_fence_remove_callback(struct dma_fence *fence,
>  			       struct dma_fence_cb *cb);
> -void dma_fence_enable_sw_signaling(struct dma_fence *fence);
> +int dma_fence_enable_sw_signaling(struct dma_fence *fence);
>  
>  /**
>   * dma_fence_is_signaled_locked - Return an indication if the fence
> -- 
> 2.34.1
> 
> 

-- 
Kees Cook