netdev - Re: veth regression with "don’t modify ip_summed; doing so treats packets with bad checksums as good."

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Date:	Thu, 24 Mar 2016 22:06:25 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Vijay Pandurangan <vijayp@...ayp.ca>,
	netdev <netdev@...r.kernel.org>, Evan Jones <ej@...njones.ca>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: veth regression with "don’t modify ip_summed; doing so treats packets with bad checksums as good."

On Thu, Mar 24, 2016 at 9:34 PM, Ben Greear <greearb@...delatech.com> wrote:
>
>
> On 03/24/2016 06:44 PM, Vijay Pandurangan wrote:
>>
>> Oops, I think my last email didn't go through due to an inadvertent
>> html attachment from my phone mail client.
>>
>> Can you send us a copy of a packet you're sending and/or confirm that
>> the IP and UDP4 checksums are set correctly in the packet?
>>
>> If those are set right, I think we need to read through the networking
>> code again to see why this is broken...
>
>
> Wireshark decodes the packet as having no checksum errors.
>
> I think the contents of the packet is correct, but the 'ip_summed'
> field is set incorrectly to 'NONE' when transmitting on a raw packet
> socket.

Yeah, these bugs are all due to the different interpretations of
ip_summed on TX path and RX path. I think the following patch
should work, if the comments don't mislead me. Could you give
it a try?

For the long term, we need to unify the meaning of ip_summed
on TX path and RX path, or at least translate it in skb_scrub_packet().

Thanks.

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 8d22de7..726457e 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -377,7 +377,7 @@ static int raw_send_hdrinc(struct sock *sk, struct
flowi4 *fl4,
        iph = ip_hdr(skb);
        skb_put(skb, length);

-       skb->ip_summed = CHECKSUM_NONE;
+       skb->ip_summed = CHECKSUM_UNNECESSARY;

        sock_tx_timestamp(sk, &skb_shinfo(skb)->tx_flags);

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 4319e65..e6b3e31 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -646,7 +646,7 @@ static int rawv6_send_hdrinc(struct sock *sk,
struct msghdr *msg, int length,
        skb_reset_network_header(skb);
        iph = ipv6_hdr(skb);

-       skb->ip_summed = CHECKSUM_NONE;
+       skb->ip_summed = CHECKSUM_UNNECESSARY;

        skb->transport_header = skb->network_header;
        err = memcpy_from_msg(iph, msg, length);