Re: [PATCH] xfrm: xfrm_input: fix a possible memory leak in xfrm_input()

[Hangyu Hua <hbh25y@gmail.com>]

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@gmail.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. 
If it return return in [2] and [4], there will not be a memory leak. It 
look like my patch is incorrect.

How do you think i modify the patch as follows?

    			gro_cells_receive(&gro_cells, skb);
    			return err;
    		}
  -
  +		if (err != 0)
  +			kfree_skb(skb);
    		return err;
    	}