linux-kernel - Re: [PATCH] nfc: st21nfca: fix possible double free in st21nfca_im_recv_dep_res

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Message-ID: <31fa8ce4-a132-03c6-3272-6f8448270830@gmail.com>
Date:   Thu, 23 Jun 2022 18:47:19 +0800
From:   Hangyu Hua <hbh25y@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, krzysztof.kozlowski@...aro.org,
        sameo@...ux.intel.com, christophe.ricard@...il.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nfc: st21nfca: fix possible double free in
 st21nfca_im_recv_dep_res_cb()

On 2022/6/23 17:42, Paolo Abeni wrote:
> On Wed, 2022-06-22 at 14:51 +0800, Hangyu Hua wrote:
>> nfc_tm_data_received will free skb internally when it fails. There is no
>> need to free skb in st21nfca_im_recv_dep_res_cb again.
>>
>> Fix this by setting skb to NULL when nfc_tm_data_received fails.
>>
>> Fixes: 1892bf844ea0 ("NFC: st21nfca: Adding P2P support to st21nfca in Initiator & Target mode")
>> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
>> ---
>>   drivers/nfc/st21nfca/dep.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/nfc/st21nfca/dep.c b/drivers/nfc/st21nfca/dep.c
>> index 1ec651e31064..07ac5688011c 100644
>> --- a/drivers/nfc/st21nfca/dep.c
>> +++ b/drivers/nfc/st21nfca/dep.c
>> @@ -594,7 +594,8 @@ static void st21nfca_im_recv_dep_res_cb(void *context, struct sk_buff *skb,
>>   			    ST21NFCA_NFC_DEP_PFB_PNI(dep_res->pfb + 1);
>>   			size++;
>>   			skb_pull(skb, size);
>> -			nfc_tm_data_received(info->hdev->ndev, skb);
>> +			if (nfc_tm_data_received(info->hdev->ndev, skb))
>> +				skb = NULL;
> 
> Note that 'skb' not used (nor freed) by this function after this point:
> the next 'break' statement refears to the inner switch, and land to the
> execution flow to the 'return' statement a few lines below.
> kfree_skb(skb) is never reached.
> 
> Paolo
> 

My fault. I messed up two switch statements. I will be more careful next 
time.

hangyu