Re: [PATCH 4.14] tcp: refine memory limit test in tcp_fragment()

[Josh Hunt <johunt@akamai.com>]

On 6/25/19 1:26 PM, Sasha Levin wrote:
> On Tue, Jun 25, 2019 at 01:19:37PM -0400, Josh Hunt wrote:
>> Backport of dad3a9314ac95dedc007bc7dacacb396ea10e376:
> 
> You probably meant b6653b3629e5b88202be3c9abc44713973f5c4b4 here.

I wasn't sure if I should reference the upstream commit or stable 
commit. dad3a9314 is the version of the commit from linux-4.14.y. There 
may be a similar issue with the Fixes tag below since that also 
references the 4.14 vers of the change.

> 
>> tcp_fragment() might be called for skbs in the write queue.
>>
>> Memory limits might have been exceeded because tcp_sendmsg() only
>> checks limits at full skb (64KB) boundaries.
>>
>> Therefore, we need to make sure tcp_fragment() wont punish applications
>> that might have setup very low SO_SNDBUF values.
>>
>> Backport notes:
>> Initial version used tcp_queue type which is not present in older 
>> kernels,
>> so added a new arg to tcp_fragment() to determine whether this is a
>> retransmit or not.
>>
>> Fixes: 9daf226ff926 ("tcp: tcp_fragment() should apply sane memory 
>> limits")
>> Signed-off-by: Josh Hunt <johunt@akamai.com>
>> Reviewed-by: Jason Baron <jbaron@akamai.com>
>> ---
>>
>> Eric/Greg - This applies on top of v4.14.130. I did not see anything come
>> through for the older (<4.19) stable kernels yet. Without this change
>> Christoph Paasch's packetrill script 
>> (https://lore.kernel.org/netdev/CALMXkpYVRxgeqarp4gnmX7GqYh1sWOAt6UaRFqYBOaaNFfZ5sw@mail.gmail.com/) 
>>
>> will fail on 4.14 stable kernels, but passes with this change.
> 
> Eric, it would be great if you could Ack this, it's very different from
> your original patch.

Yes, that would be great.

Josh

> 
> -- 
> Thanks,
> Sasha