linux-kernel - Re: nfc: nci: fix potential NULL pointer dereference

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Message-ID: <20170612172805.Horde.AUST5RGJfhNVnchxoXV3U2C@gator4166.hostgator.com>
Date:   Mon, 12 Jun 2017 17:28:05 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Samuel Ortiz <sameo@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: nfc: nci: fix potential NULL pointer dereference

Hi Guenter,

Please, see my comments below

Quoting Guenter Roeck <linux@...ck-us.net>:

> On Mon, Jun 12, 2017 at 05:02:23PM -0500, Gustavo A. R. Silva wrote:
>> NULL check at line 76: if (conn_info) {, implies that pointer conn_info
>> might be NULL, but this pointer is being previously dereferenced,
>> which might cause a NULL pointer dereference.
>>
>> Add NULL check before dereferencing pointer conn_info in order to
>> avoid a potential NULL pointer dereference.
>>
>> Addresses-Coverity-ID: 1362349
>> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
>> ---
>>  net/nfc/nci/core.c | 11 +++++------
>>  1 file changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
>> index 61fff42..d2198ce 100644
>> --- a/net/nfc/nci/core.c
>> +++ b/net/nfc/nci/core.c
>> @@ -70,14 +70,13 @@ int  
>> nci_get_conn_info_by_dest_type_params(struct nci_dev *ndev, u8  
>> dest_type,
>>  	struct nci_conn_info *conn_info;
>>
>>  	list_for_each_entry(conn_info, &ndev->conn_info_list, list) {
>
> conn_info is set in list_for_each_entry() using container_of(),
> which is never NULL. Plus, it is dereferenced there as well.
> The check is unnecessary.
>

Thanks for clarifying.

> Guenter
>
>> -		if (conn_info->dest_type == dest_type) {
>> +		if (conn_info && conn_info->dest_type == dest_type) {
>>  			if (!params)
>>  				return conn_info->conn_id;
>> -			if (conn_info) {

So, this NULL check could be removed as it seems it is not useful at all ?

>> -				if (params->id == conn_info->dest_params->id &&
>> -				    params->protocol == conn_info->dest_params->protocol)
>> -					return conn_info->conn_id;
>> -			}
>> +
>> +			if (params->id == conn_info->dest_params->id &&
>> +			    params->protocol == conn_info->dest_params->protocol)
>> +				return conn_info->conn_id;
>>  		}
>>  	}
>>

Thank you
--
Gustavo A. R. Silva