linux-kernel - Re: [PATCH] ata: dwc_460ex: Avoid potential NULL pointer dereference

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Message-ID: <17a6d83b-c57e-b709-7443-302b84692a6d@umn.edu>
Date:   Sun, 24 Mar 2019 11:47:03 -0500
From:   Aditya Pakki <pakki001@....edu>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     kjlu@....edu, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ata: dwc_460ex: Avoid potential NULL pointer dereference

On 3/24/19 11:28 AM, Jens Axboe wrote:
> On 3/4/19 4:08 PM, Aditya Pakki wrote:
>> dma_async_tx_descriptor can contain a NULL variable and using
>> it in dmaengine_submit without checking can crash the process.
>> This patch avoids such a scenario.
>>
>> Signed-off-by: Aditya Pakki <pakki001@....edu>
>> ---
>>  drivers/ata/sata_dwc_460ex.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/ata/sata_dwc_460ex.c b/drivers/ata/sata_dwc_460ex.c
>> index 6f142aa54f5f..44a0d7a1ef54 100644
>> --- a/drivers/ata/sata_dwc_460ex.c
>> +++ b/drivers/ata/sata_dwc_460ex.c
>> @@ -1052,8 +1052,10 @@ static void sata_dwc_bmdma_start_by_tag(struct ata_queued_cmd *qc, u8 tag)
>>  					SATA_DWC_DMACR_RXCHEN);
>>  
>>  		/* Enable AHB DMA transfer on the specified channel */
>> -		dmaengine_submit(desc);
>> -		dma_async_issue_pending(hsdevp->chan);
>> +		if (desc) {
>> +			dmaengine_submit(desc);
>> +			dma_async_issue_pending(hsdevp->chan);
>> +		}
>>  	}
>>  }
> 
> Hmm, if desc == NULL, is that an error condition?
> 
Jens,
In dmaengine_submit, the desc variable is dereferenced without a check for NULL.