Re: [PATCH net-next 1/3] ipv6: Clear flush_id to make GRO work

On Tue, Sep 9, 2014 at 11:38 AM, Eric Dumazet [off-list ref] wrote:

On Tue, 2014-09-09 at 11:23 -0700, Tom Herbert wrote:

quoted

In TCP gro we check flush_id which is derived from the IP identifier.
In IPv4 gro path the flush_id is set with the expectation that every
matched packet increments IP identifier. In IPv6, the flush_id is
never set and thus is uinitialized. What's worse is that in IPv6
over IPv4 encapsulation, the IP identifier is taken from the outer
header which is currently not incremented on every packet for Linux
stack, so GRO in this case never matches packets (identifier is
not increasing).

This patch clears flush_id for every time for a matched packet in
IPv6 gro_receive. We need to do this each time to overwrite the
setting that would be done in IPv4 gro_receive per the outer
header in IPv6 over Ipv4 encapsulation.

Signed-off-by: Tom Herbert <redacted>
---
 net/ipv6/ip6_offload.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index 5bcda33..929bbbcd 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c

@@ -261,6 +261,9 @@ static struct sk_buff **ipv6_gro_receive(struct sk_buff **head,
              /* flush if Traffic Class fields are different */
              NAPI_GRO_CB(p)->flush |= !!(first_word & htonl(0x0FF00000));
              NAPI_GRO_CB(p)->flush |= flush;
+
+             /* Clear flush_id, there's really no concept of ID in IPv6. */
+             NAPI_GRO_CB(p)->flush_id = 0;
      }

      NAPI_GRO_CB(skb)->flush |= flush;

Yeah, I mentioned this problem months ago and apparently forgot to push
the fix.

Unfortunately, probably not the last GRO issue. This whole thing is
really rather fragile and probably easy to break undetected...

http://patchwork.ozlabs.org/patch/311212/

Signed-off-by: Eric Dumazet <edumazet@google.com>