Messages in this thread | | | Date | Thu, 28 Apr 2016 06:45:50 -0700 | From | Ben Greear <> | Subject | Re: [PATCH 3.2 085/115] veth: don’t modify ip summed; doing so treats packets with bad checks ums as good. |
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On 04/28/2016 03:29 AM, Sabrina Dubroca wrote: > Hello, > > 2016-04-27, 17:14:44 -0700, Ben Greear wrote: >> On 04/27/2016 05:00 PM, Hannes Frederic Sowa wrote: >>> Hi Ben, >>> >>> On Wed, Apr 27, 2016, at 20:07, Ben Hutchings wrote: >>>> On Wed, 2016-04-27 at 08:59 -0700, Ben Greear wrote: >>>>> On 04/26/2016 04:02 PM, Ben Hutchings wrote: >>>>>> >>>>>> 3.2.80-rc1 review patch. If anyone has any objections, please let me know. >>>>> I would be careful about this. It causes regressions when sending >>>>> PACKET_SOCKET buffers from user-space to veth devices. >>>>> >>>>> There was a proposed upstream fix for the regression, but it has not gone >>>>> into the tree as far as I know. >>>>> >>>>> http://www.spinics.net/lists/netdev/msg370436.html >>>> [...] >>>> >>>> OK, I'll drop this for now. >>> >>> The fall out from not having this patch is in my opinion a bigger >>> fallout than not having this patch. This patch fixes silent data >>> corruption vs. the problem Ben Greear is talking about, which might not >>> be that a common usage. >>> >>> What do others think? >>> >>> Bye, >>> Hannes >>> >> >> This patch from Cong Wang seems to fix the regression for me, I think it should be added and >> tested in the main tree, and then apply them to stable as a pair. >> >> http://dmz2.candelatech.com/?p=linux-4.4.dev.y/.git;a=commitdiff;h=8153e983c0e5eba1aafe1fc296248ed2a553f1ac;hp=454b07405d694dad52e7f41af5816eed0190da8a > > Actually, no, this is not really a regression. > > If you capture packets on a device with checksum offloading enabled, > the TCP/UDP checksum isn't filled. veth also behaves that way. What > the "veth: don't modify ip_summed" patch does is enable proper > checksum validation on veth. This really was a bug in veth. > > Cong's patch would also break cases where we choose to inject packets > with invalid checksums, and they would now be accepted as correct. > > Your use case is invalid, it just happened to work because of a > bug. If you want the stack to fill checksums so that you want capture > and reinject packets, you have to disable checksum offloading (or > compute the checksum yourself in userspace).
Disabling checksum offloading or computing in user-space (and then recomputing in veth to verify the checksum?) is a huge performance loss.
Maybe we could add a socket option to enable Cong's patch on a per-socket basis? That way my use-case can still work and you can have this new behaviour by default?
Thanks, Ben
-- Ben Greear <greearb@candelatech.com> Candela Technologies Inc http://www.candelatech.com
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