Re: [PATCH] net: tcp: ipv6_mapped needs sk_rx_dst_set method

On Sun, Aug 19, 2012 at 12:06:33AM -0400, Neal Cardwell wrote:

On Sat, Aug 18, 2012 at 9:06 AM, Artem Savkov [off-list ref] wrote:

quoted

[ 1699.195040] EIP is at inet6_sk_rx_dst_set+0x40/0xa0

...

quoted

[ 1699.198736]  [<c15662a1>] tcp_create_openreq_child+0x41/0x4e0
[ 1699.198884]  [<c1563b54>] tcp_v4_syn_recv_sock+0x34/0x330
[ 1699.199032]  [<c15d162e>] tcp_v6_syn_recv_sock+0x3fe/0x660

...

quoted

[ 1699.242913] EIP: [<c15d11d0>] inet6_sk_rx_dst_set+0x40/0xa0 SS:ESP 0068:f540dce0
[ 1699.245945] CR2: 0000000000000016
[ 1699.280708] ---[ end trace 3fb05aeec95e7238 ]---
[ 1699.280806] Kernel panic - not syncing: Fatal exception in interrupt
[ 1699.284674] panic occurred, switching back to text console

Thanks for the detailed report!

I don't think that particular fix is kosher, since this basically
changes the address family ops of the parent listening socket ('sk'
here).The parent listening socket needs to keep its IPv6 af_ops so its
IPv6 children can get the right af_ops.

Indeed, my approach breaks ipv6 after first mapped connection.

We should probably either: (a) make sure the af_ops of the child
socket are set correctly earlier, or (b) not use dynamic dispatch
through the af_ops within tcp_create_openreq_child(), and just do the
sk_rx_dst_set a tiny bit later. I've sent out a patch for approach (b)
here, since it's simpler:

  http://patchwork.ozlabs.org/patch/178525/

I've verified that IPv4, IPv6, and IPv4-mapped-IPv6 connections work
for me with this patch. But if you could test it as well, that would
be great.

I've tested it and can confirm that all three connection types work.
Thank you for the patch and explanation.

-- 
Kind regards,
Artem