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SubjectRe: [PATCH] xfrm: xfrm_input: fix a possible memory leak in xfrm_input()
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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;
}



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