Re: [lvc-project] [PATCH] netfilter: nfnetlink: NULL-check skb->dev in __build_packet_message()

["Igor A. Artemiev" <Igor.A.Artemiev@mcst.ru>]

On 3/27/23 13:22, Pablo Neira Ayuso wrote:
> On Mon, Mar 27, 2023 at 12:41:16PM +0300, Igor Artemiev wrote:
>> After having been compared to NULL value at nfnetlink_log.c:560,
>> pointer 'skb->dev' is dereferenced at nfnetlink_log.c:576.
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Signed-off-by: Igor Artemiev <Igor.A.Artemiev@mcst.ru>
>> ---
>>   net/netfilter/nfnetlink_log.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
>> index d97eb280cb2e..2711509eb9a5 100644
>> --- a/net/netfilter/nfnetlink_log.c
>> +++ b/net/netfilter/nfnetlink_log.c
>> @@ -572,7 +572,7 @@ __build_packet_message(struct nfnl_log_net *log,
>>   		}
>>   	}
>>   
>> -	if (indev && skb_mac_header_was_set(skb)) {
>> +	if (indev && skb->dev && skb_mac_header_was_set(skb)) {
> This cannot ever happen, we assume skb->dev is always set on.
>
>>   		if (nla_put_be16(inst->skb, NFULA_HWTYPE, htons(skb->dev->type)) ||
>>   		    nla_put_be16(inst->skb, NFULA_HWLEN,
>>   				 htons(skb->dev->hard_header_len)))
>> -- 
>> 2.30.2
>>

If skb->dev is always set on, should the check at nfnetlink_log.c:560 be removed?
|

if  (indev  &&  skb->dev  &&
	skb_mac_header_was_set(skb)  &&
	    	skb_mac_header_len(skb)  !=  0)  { |

||Thanks, Igor