netdev - Re: [PATCH net] enic: fix rx skb checksum

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20141219120757.106c02d4@griffin>
Date:	Fri, 19 Dec 2014 12:07:57 +0100
From:	Jiri Benc <jbenc@...hat.com>
To:	Govindarajulu Varadarajan <_govind@....com>
Cc:	Jay Vosburgh <jay.vosburgh@...onical.com>,
	Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
	netdev@...r.kernel.org, ssujith@...co.com, benve@...co.com,
	Stefan Assmann <sassmann@...hat.com>
Subject: Re: [PATCH net] enic: fix rx skb checksum

On Fri, 19 Dec 2014 16:22:34 +0530 (IST), Govindarajulu Varadarajan wrote:
> Hardware returns 0xffff for non tcp/udp packets.

That explains that I saw that with ICMP packets.

> For tcp/udp packet it returns
> pseudo checksum. Not the _whole_ pkt checksum.

I see. I didn't get this from your patch, although you wrote it there,
sorry. And I didn't dig that deep while debugging, I was satisfied with
seeing 0xffff for the packets that caused problems :-)

> Dec 18 11:13:18 a163 kernel: enic: saddr=96d8690a, daddr=a3ba6a0a, length=40, proto=6
> Dec 18 11:13:18 a163 kernel: enic: hw_checksum = c457, pseudo_checksum_32=3a930115, pseudo_checksum_fold=c457
> 
> Dec 18 11:13:18 a163 kernel: enic: saddr=a37410a, daddr=a3ba6a0a, length=32, proto=6
> Dec 18 11:13:18 a163 kernel: enic: hw_checksum = 80f9, pseudo_checksum_32=adf1d114, pseudo_checksum_fold=80f9
> 
> Dec 18 11:13:18 a163 kernel: enic: saddr=a37410a, daddr=a3ba6a0a, length=32, proto=6
> Dec 18 11:13:18 a163 kernel: enic: hw_checksum = 80f9, pseudo_checksum_32=adf1d114, pseudo_checksum_fold=80f9
> 
> Clearly hw is returning folded pseudo checksum.

Indeed.

> > I have no idea whether the hardware verified the checksum for the
> > 0xffff case and is just not returning the checksum or whether such
> > packets come completely unverified.
> 
> Yes, hardware verifies the checksum and sets tcp_udp_csum_ok flag to 1.
> If pkt verification fails or pkt is not tcp/udp, tcp_udp_csum_ok is 0. And we
> send the pkt to stack with CHECKSUM_NONE.

Thanks for the confirmation.

> Driver should use CHECKSUM_COMPLETE only if it can produce _whole_ pkt checksum.
> as described in include/linux/skbuff.h:75

Sure. I just misunderstood what the hardware provides.

> I am trying to fix "Do not set CHECKSUM_COMPLETE, when driver does not have
> checksum of whole pkt."
> 
> Is my understanding correct?

With the information you've just written (thanks for your patience),
I think your patch is correct.

Thanks a lot!

 Jiri

-- 
Jiri Benc
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html