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

[Eric Dumazet]

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)