netdev - Re: kTLS broken somewhere between 4.18 and 5.0

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Message-ID: <f832cd50-50c5-027c-51db-8a3a3ded4563@gmail.com>
Date:   Sun, 14 Apr 2019 13:40:20 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Andre Tomt <andre@...t.net>,
        "Steinar H. Gunderson" <steinar+kernel@...derson.no>,
        netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>
Subject: Re: kTLS broken somewhere between 4.18 and 5.0

On 4/13/19 6:56 PM, Andre Tomt wrote:
> On 13.04.2019 17:34, Steinar H. Gunderson wrote:
>> Hi,
>>
>> I've been using kTLS for a while, with my video reflector Cubemap
>> (https://git.sesse.net/?p=cubemap). After I upgraded my server from
>> 4.18.11 to 5.0.6, seemingly I've started seeing corruption. The data sent
>> with send() (HTTP headers, HLS playlists) appears to be fine, but sendfile()
>> (actual video data, from a file on tmpfs) is not; after ~20 kB of data
>> (19626 in one test here), the data appears to be randomly corrupted. Diffing
>> non-TLS (good) and TLS (bad) video data:
>>
>>    00004c70: fa 70 c5 71 b5 f5 b7 ac 74 b0 ca 80 02 4c 06 3f  .p.q....t....L.?
>>    00004c80: 5c 5b 0c b3 e0 a0 c3 21 93 d3 6e 65 36 70 0a 27  \[.....!..ne6p.'
>>    00004c90: 84 67 16 2c 95 c0 55 e1 04 76 52 10 50 5d 00 26  .g.,..U..vR.P].&
>>
>>   -00004ca0: 0c b8 84 70 7e ed 12 8f 5e 7e 18 c0 06 20 02 54  ...p~...^~... .T
>>   +00004ca0: 0c b8 84 70 7e ed 12 8f 5e 7e 0a 60 9f 1f 97 f2  ...p~...^~.`....
>>
>>   -00004cb0: 1e 4c c1 71 7d 0b 91 28 23 98 09 ae c4 95 ae 7f  .L.q}..(#.......
>>   +00004cb0: 6e 17 50 03 67 fa 2f 83 b0 88 eb fc 54 f2 0b 00  n.P.g./.....T...
>>
>>   -00004cc0: a2 92 20 b8 f2 b6 72 2a e8 7e d7 27 99 65 56 70  .. ...r*.~.'.eVp
>>   +00004cc0: 6c 9e a1 02 b4 30 11 25 d7 58 b0 0c c0 6c e1 bd  l....0.%.X...l..
>>
>> It never appears to get back into sync after that. Interestingly, it is
>> _consistently_ wrong; if I download the same fragment multiple times, it
>> breaks at the same place and gives the same garbage (but different fragments
>> give different divergence points). Tested with both wget and Chrome.
>> Does anyone know what could be wrong?
>>
>> (It is, unfortunately, not easy for me to reboot this server at will, so a
>> bisect could be hard.)
>>
>> Please Cc me on any replies, I'm not subscribed to netdev.
>>
>> /* Steinar */
>>
> 
> 
> Reproduced and bisected, the problem showed up in v4.20-rc1. Unfortunately the commit seems to have some significant dependencies so I was unable to verify by reverting it on 4.20.
> 


Hi thanks I'll take a look this evening or first thing tomorrow. I have
a couple other fixes queued up for ktls as well so I'll see if we can get
a fix for this included in that series.

Thanks!
John