On 7/08/2020 16:47, Sabrina Dubroca wrote:
> 2020-08-04, 14:32:56 +0200, Bram Yvakh wrote:
>
>> On 4/08/2020 11:37, Sabrina Dubroca wrote:
>>
>>> diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
>>> index b615729812e5..ade2eba863b3 100644
>>> --- a/net/xfrm/xfrm_interface.c
>>> +++ b/net/xfrm/xfrm_interface.c
>>> @@ -292,7 +292,7 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device
>>> *dev, struct flowi *fl)
>>> }
>>>
>>> mtu = dst_mtu(dst);
>>> - if (!skb->ignore_df && skb->len > mtu) {
>>> + if (skb->len > mtu) {
>>>
[snip]
>
> Yeah, it's the most simple xfrmi setup possible (directly connected by
> a veth),
Thanks, that gives me something to experiment with;
Could you you share what kernel your testing with? (i.e. what
tree/branch/sha)
> and just run ping on it. ping sets DF, we want an exception
> to be created, but this test prevents it.
>
As I said dropping the test currently doesn't make sense to me.
I would expect that the 'ignore_df' flag is not set on the device, and
if it's set then I would expect things to work.
> The packet ends up being dropped in xfrm_output_one because of the mtu
> check in xfrm4_tunnel_check_size.
>
That's the bit that does not (yet) make senes to me..
Looking at net-next/master (bfdd5aaa54b0a44d9df550fe4c9db7e1470a11b8)
||
static int xfrm4_tunnel_check_size(struct sk_buff *skb)
{
int mtu, ret = 0;
if (IPCB(skb)->flags & IPSKB_XFRM_TUNNEL_SIZE)
goto out;
if (!(ip_hdr(skb)->frag_off & htons(IP_DF)) || skb->ignore_df)
goto out;
mtu = dst_mtu(skb_dst(skb));
if ((!skb_is_gso(skb) && skb->len > mtu) ||
(skb_is_gso(skb) &&
!skb_gso_validate_network_len(skb, ip_skb_dst_mtu(skb->sk,
skb)))) {
skb->protocol = htons(ETH_P_IP);
if (skb->sk)
xfrm_local_error(skb, mtu);
else
icmp_send(skb, ICMP_DEST_UNREACH,
ICMP_FRAG_NEEDED, htonl(mtu));
ret = -EMSGSIZE;
}
out:
return ret;
}
*If* skb->ignore_df is set then it *skips* the mtu check.
In other words: 'xfrm4_tunnel_check_size' only cares about the mtu if ignore_df
isn't set.
The original code in 'xfrmi_xmit2': only checks the mtu if ignore_df isn't set.
(-> looks consistent)
With your patch: 'xfrmi_xmit2' now always checks the mtu whereas
'xfrm4_tunnel_check_size' only checks it when ignore_df isn't set.
