netdev - Re: [PATCH] netfilter: nfnetlink: check 'skb->dev' pointer in nfulnl_log

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Date:   Mon, 5 Dec 2022 15:28:07 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Li Qiong <liqiong@...china.com>
Cc:     Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, coreteam@...filter.org,
        Yu Zhe <yuzhe@...china.com>
Subject: Re: [PATCH] netfilter: nfnetlink: check 'skb->dev' pointer in
 nfulnl_log_packet()

On Fri, Dec 02, 2022 at 04:33:04PM +0800, Li Qiong wrote:
> The 'skb->dev' may be NULL, it should be better to check it.
> 
> Signed-off-by: Li Qiong <liqiong@...china.com>
> ---
>  net/netfilter/nfnetlink_log.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
> index d97eb280cb2e..74ac9fa40137 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)) {
>  		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)))
> @@ -724,7 +724,7 @@ nfulnl_log_packet(struct net *net,
>  		+ nla_total_size(sizeof(struct nfulnl_msg_packet_timestamp))
>  		+ nla_total_size(sizeof(struct nfgenmsg));	/* NLMSG_DONE */
>  
> -	if (in && skb_mac_header_was_set(skb)) {
> +	if (in && skb->dev && skb_mac_header_was_set(skb)) {
>  		size += nla_total_size(skb->dev->hard_header_len)
>  			+ nla_total_size(sizeof(u_int16_t))	/* hwtype */
>  			+ nla_total_size(sizeof(u_int16_t));	/* hwlen */

skb->dev is always guaranteed to be set in this path.