netdev - Re: [PATCH] xfrm: xfrm_input: fix a possible memory leak in xfrm

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Date:   Wed, 1 Jun 2022 10:47:15 +0800
From:   Hangyu Hua <hbh25y@...il.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfrm: xfrm_input: fix a possible memory leak in
 xfrm_input()

On 2022/5/31 19:35, Steffen Klassert wrote:
> On Tue, May 31, 2022 at 10:12:05AM +0800, Hangyu Hua wrote:
>> On 2022/5/30 18:37, Steffen Klassert wrote:
>>> On Mon, May 30, 2022 at 06:20:46PM +0800, Hangyu Hua wrote:
>>>> xfrm_input needs to handle skb internally. But skb is not freed When
>>>> xo->flags & XFRM_GRO == 0 and decaps == 0.
>>>>
>>>> Fixes: 7785bba299a8 ("esp: Add a software GRO codepath")
>>>> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
>>>> ---
>>>>    net/xfrm/xfrm_input.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
>>>> index 144238a50f3d..6f9576352f30 100644
>>>> --- a/net/xfrm/xfrm_input.c
>>>> +++ b/net/xfrm/xfrm_input.c
>>>> @@ -742,7 +742,7 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
>>>>    			gro_cells_receive(&gro_cells, skb);
>>>>    			return err;
>>>>    		}
>>>> -
>>>> +		kfree_skb(skb);
>>>>    		return err;
>>>>    	}
>>>
>>> Did you test this? The function behind the 'afinfo->the transport_finish()'
>>> pointer handles this skb and frees it in that case.
>>
>> int xfrm4_transport_finish(struct sk_buff *skb, int async)
>> {
>> 	struct xfrm_offload *xo = xfrm_offload(skb);
>> 	struct iphdr *iph = ip_hdr(skb);
>>
>> 	iph->protocol = XFRM_MODE_SKB_CB(skb)->protocol;
>>
>> #ifndef CONFIG_NETFILTER
>> 	if (!async)
>> 		return -iph->protocol;		<--- [1]
>> #endif
>> ...
>> 	NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING,
>> 		dev_net(skb->dev), NULL, skb, skb->dev, NULL,
>> 		xfrm4_rcv_encap_finish);	<--- [2]
>> 	return 0;
>> }
>>
>> int xfrm6_transport_finish(struct sk_buff *skb, int async)
>> {
>> 	struct xfrm_offload *xo = xfrm_offload(skb);
>> 	int nhlen = skb->data - skb_network_header(skb);
>>
>> 	skb_network_header(skb)[IP6CB(skb)->nhoff] =
>> 		XFRM_MODE_SKB_CB(skb)->protocol;
>>
>> #ifndef CONFIG_NETFILTER
>> 	if (!async)
>> 		return 1;			<--- [3]
>> #endif
>> ...
>> 	NF_HOOK(NFPROTO_IPV6, NF_INET_PRE_ROUTING,
>> 		dev_net(skb->dev), NULL, skb, skb->dev, NULL,
>> 		xfrm6_transport_finish2);
>> 	return 0;				<--- [4]
>> }
>>
>> If transport_finish() return in [1] or [3], there will be a memory leak.
> 
> No, even in that case there is no memleak. Look for instance at the
> IPv4 case, we return -iph->protocol here.
> Then look at ip_protocol_deliver_rcu(). If the ipprot->handler (xfrm)
> returns a negative value, this is interpreted as the protocol number
> and the packet is resubmitted to the next protocol handler.
> 
> Please test your patches before you submit them in the future.
Thanks for your explanation. I will be more careful in the future.