Re: [PATCH net] tcp: initialize standalone IPv4 ACK options

[Yizhou Zhao]

Thanks for your review.

> On Jul 13, 2026, at 16:48, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> 
> On Mon, Jul 13, 2026 at 10:18 AM Yizhou Zhao
> <zhaoyz24@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> 
>> tcp_v4_send_ack() constructs standalone IPv4 TCP ACK replies on the stack
>> for SYN-RECV and TIME-WAIT paths.  It currently zeroes only the TCP
>> header, not the accompanying option buffer.
>> 
>> TCP-AO options may have actual lengths that are not 4-byte aligned, while
>> the transmitted TCP header length is correctly rounded up to a 4-byte
>> boundary.  tcp_ao_hash_hdr() writes only the MAC bytes, leaving the
>> TCP-AO option alignment padding in rep.opt uninitialized.  With stack
>> auto-initialization disabled, those padding bytes can be copied into the
>> network packet and sent to the peer.
>> 
>> Zero the whole reply structure before writing options, so the alignment
>> padding bytes are initialized.
> 
> Please fix TCP-AO instead of slowing down TCP (almost no TCP flow is using AO)

We have posted a v2 patch following your suggestions:
https://lore.kernel.org/netdev/20260713105631.8616-1-zhaoyz24@xxxxxxxxxxxxxxxxxxxxx/

Regards,
Yizhou