linux-kernel - Re: [PATCH][next] dma-buf: Fix NULL pointer dereference in dma_fence_enable_sw

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Date:   Wed, 11 Oct 2023 10:13:42 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        Arvind Yadav <Arvind.Yadav@....com>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] dma-buf: Fix NULL pointer dereference in
 dma_fence_enable_sw_signaling()



On 10/11/23 10:03, Kees Cook wrote:
> 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?

Nope. I would have to add a `goto` to skip `dma_fence_enable_sw_signaling(chain)`.

I originally thought of that, but as other _signaling() functions have
sanity-checks inside, I decided to go with that solution.

This bug has been there since Sep 2022. So, adding a sanity check inside that
function should prevent any other issue of this same kind to enter the codebase
and stay there for years.

--
Gustavo

> 
> -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@...r.kernel.org
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.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
>>
>>
>