linux-kernel - Re: [lvc-project] [PATCH] netfilter: nfnetlink: NULL-check skb->dev in __build_packet

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Message-ID: <ZCFuaDrSdsyzRdgJ@salvia>
Date:   Mon, 27 Mar 2023 12:22:32 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Igor Artemiev <Igor.A.Artemiev@...t.ru>
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>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [lvc-project] [PATCH] netfilter: nfnetlink: NULL-check skb->dev
 in __build_packet_message()

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@...t.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
>