Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH net] net: gro: set the last skb->next to NULL when it get
 merged
To:     kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org,
        alobakin@pm.me, jonathan.lemon@gmail.com, willemb@google.com,
        pabeni@redhat.com, vvs@virtuozzo.com, cong.wang@bytedance.com
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jason Xing <xingwanli@kuaishou.com>
References: <20211026131859.59114-1-kerneljasonxing@gmail.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <2b839087-ed6a-d498-e1ab-c6bcea2f2965@gmail.com>
Date:   Wed, 27 Oct 2021 12:20:04 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.14.0
MIME-Version: 1.0
In-Reply-To: <20211026131859.59114-1-kerneljasonxing@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 10/26/21 6:18 AM, kerneljasonxing@gmail.com wrote:
> From: Jason Xing <xingwanli@kuaishou.com>
> 
> Setting the @next of the last skb to NULL to prevent the panic in future
> when someone does something to the last of the gro list but its @next is
> invalid.
> 
> For example, without the fix (commit: ece23711dd95), a panic could happen
> with the clsact loaded when skb is redirected and then validated in
> validate_xmit_skb_list() which could access the error addr of the @next
> of the last skb. Thus, "general protection fault" would appear after that.
> 

If this a bug, please provide a Fixes: tag

> Signed-off-by: Jason Xing <xingwanli@kuaishou.com>
> ---
>  net/core/skbuff.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 2170bea..7b248f1 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4396,6 +4396,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
>  		skb_shinfo(p)->frag_list = skb;
>  	else
>  		NAPI_GRO_CB(p)->last->next = skb;
> +	skb->next = NULL;

Really at this point skb->next must be already NULL.

Please provide a stack trace so that we fix the caller instead
of adding more code in GRO layer.


>  	NAPI_GRO_CB(p)->last = skb;
>  	__skb_header_release(skb);
>  	lp = p;
>