netdev - RE: [PATCH net v4 1/1] openvswitch: Fix setting ipv6 fields causing hw csum failure

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: <6dad3593d88d4afcae331b1225888884@AcuMS.aculab.com>
Date:   Sun, 20 Feb 2022 18:38:32 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Paul Blakey' <paulb@...dia.com>,
        "dev@...nvswitch.org" <dev@...nvswitch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Pravin B Shelar <pshelar@....org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eelco Chaudron <echaudro@...hat.com>
CC:     Oz Shlomo <ozsh@...dia.com>, Vlad Buslov <vladbu@...dia.com>,
        Roi Dayan <roid@...dia.com>,
        Ariel Levkovich <lariel@...dia.com>
Subject: RE: [PATCH net v4 1/1] openvswitch: Fix setting ipv6 fields causing
 hw csum failure

From: Paul Blakey
> Sent: 20 February 2022 13:21
> 
> Ipv6 ttl, label and tos fields are modified without first
> pulling/pushing the ipv6 header, which would have updated
> the hw csum (if available). This might cause csum validation
> when sending the packet to the stack, as can be seen in
> the trace below.
> 
> Fix this by updating skb->csum if available.
...
> +static inline __wsum
> +csum_block_replace(__wsum csum, __wsum old, __wsum new, int offset)
> +{
> +	return csum_block_add(csum_block_sub(csum, old, offset), new, offset);
> +}

That look computationally OTT for sub 32bit adjustments.

It ought to be enough to do:
	return csum_add(old_csum, 0xf0000fff + new - old);

Although it will need 'tweaking' for odd aligned 24bit values.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)