veth-do-not-modify-ip_summed.patch

   1 From ce8c839b74e3017996fad4e1b7ba2e2625ede82f Mon Sep 17 00:00:00 2001
   2 From: Vijay Pandurangan <vijayp@vijayp.ca>
   3 Date: Fri, 18 Dec 2015 14:34:59 -0500
   4 Subject: =?UTF-8?q?veth:=20don=E2=80=99t=20modify=20ip=5Fsummed;=20doing?=
   5  =?UTF-8?q?=20so=20treats=20packets=20with=20bad=20checksums=20as=20good.?=
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   9
  10 Packets that arrive from real hardware devices have ip_summed ==
  11 CHECKSUM_UNNECESSARY if the hardware verified the checksums, or
  12 CHECKSUM_NONE if the packet is bad or it was unable to verify it. The
  13 current version of veth will replace CHECKSUM_NONE with
  14 CHECKSUM_UNNECESSARY, which causes corrupt packets routed from hardware to
  15 a veth device to be delivered to the application. This caused applications
  16 at Twitter to receive corrupt data when network hardware was corrupting
  17 packets.
  18
  19 We believe this was added as an optimization to skip computing and
  20 verifying checksums for communication between containers. However, locally
  21 generated packets have ip_summed == CHECKSUM_PARTIAL, so the code as
  22 written does nothing for them. As far as we can tell, after removing this
  23 code, these packets are transmitted from one stack to another unmodified
  24 (tcpdump shows invalid checksums on both sides, as expected), and they are
  25 delivered correctly to applications. We didn’t test every possible network
  26 configuration, but we tried a few common ones such as bridging containers,
  27 using NAT between the host and a container, and routing from hardware
  28 devices to containers. We have effectively deployed this in production at
  29 Twitter (by disabling RX checksum offloading on veth devices).
  30
  31 This code dates back to the first version of the driver, commit
  32 <e314dbdc1c0dc6a548ecf> ("[NET]: Virtual ethernet device driver"), so I
  33 suspect this bug occurred mostly because the driver API has evolved
  34 significantly since then. Commit <0b7967503dc97864f283a> ("net/veth: Fix
  35 packet checksumming") (in December 2010) fixed this for packets that get
  36 created locally and sent to hardware devices, by not changing
  37 CHECKSUM_PARTIAL. However, the same issue still occurs for packets coming
  38 in from hardware devices.
  39
  40 Co-authored-by: Evan Jones <ej@evanjones.ca>
  41 Signed-off-by: Evan Jones <ej@evanjones.ca>
  42 Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
  43 Cc: Phil Sutter <phil@nwl.cc>
  44 Cc: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
  45 Cc: netdev@vger.kernel.org
  46 Cc: linux-kernel@vger.kernel.org
  47 Signed-off-by: Vijay Pandurangan <vijayp@vijayp.ca>
  48 Acked-by: Cong Wang <cwang@twopensource.com>
  49 Signed-off-by: David S. Miller <davem@davemloft.net>
  50 ---
  51  drivers/net/veth.c | 6 ------
  52  1 file changed, 6 deletions(-)
  53
  54 diff --git a/drivers/net/veth.c b/drivers/net/veth.c
  55 index 0ef4a5a..ba21d07 100644
  56 --- a/drivers/net/veth.c
  57 +++ b/drivers/net/veth.c
  58 @@ -117,12 +117,6 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
  59                 kfree_skb(skb);
  60                 goto drop;
  61         }
  62 -       /* don't change ip_summed == CHECKSUM_PARTIAL, as that
  63 -        * will cause bad checksum on forwarded packets
  64 -        */
  65 -       if (skb->ip_summed == CHECKSUM_NONE &&
  66 -           rcv->features & NETIF_F_RXCSUM)
  67 -               skb->ip_summed = CHECKSUM_UNNECESSARY;
  68
  69         if (likely(dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) {
  70                 struct pcpu_vstats *stats = this_cpu_ptr(dev->vstats);
  71 --
  72 cgit v0.12
  73