From: Jan Klemkow <jan@openbsd.org>
Subject: Re: tcp softlro ethernet padding
To: Alexander Bluhm <bluhm@openbsd.org>
Cc: tech@openbsd.org
Date: Mon, 28 Apr 2025 22:24:55 +0200

On Mon, Apr 28, 2025 at 09:04:44PM +0200, Alexander Bluhm wrote:
> Back then when I was debugging ix(4) LRO, I found that the RX mbuf
> returned from the driver may contain ethernet padding.  My tests
> did not see this behavior with ixl(4) hardware.  But inserting
> ethernet padding into a TCP stream would be completely wrong, so I
> suggest adding this sanity check.
> 
> ok?

ok jan

> Index: netinet/tcp_input.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/tcp_input.c,v
> diff -u -p -r1.440 tcp_input.c
> --- netinet/tcp_input.c	23 Apr 2025 17:52:12 -0000	1.440
> +++ netinet/tcp_input.c	28 Apr 2025 18:57:48 -0000
> @@ -4453,6 +4453,18 @@ tcp_softlro_glue(struct mbuf_list *ml, s
>  		goto out;
>  
>  	ether_extract_headers(mtail, &tail);
> +
> +	if (tail.tcp) {
> +		int tcpdatalen;
> +
> +		/* Remove possible ethernet padding at the end. */
> +		tcpdatalen = tail.iplen - tail.iphlen - tail.tcphlen;
> +		if (tcpdatalen < tail.paylen ) {
> +			m_adj(mtail, tcpdatalen - tail.paylen);
> +			tail.paylen = tcpdatalen;
> +		}
> +	}
> +
>  	if (!tcp_softlro_check(mtail, &tail)) {
>  		mtail->m_pkthdr.ph_mss = 0;
>  		goto out;
>