netdev - Re: [PATCH iwl-net] selftests/net: Fix csum test for short packets

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Message-ID: <66c5fa663e274_dc0c22942f@willemb.c.googlers.com.notmuch>
Date: Wed, 21 Aug 2024 10:32:06 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Krzysztof Galazka <krzysztof.galazka@...el.com>, 
 intel-wired-lan@...ts.osuosl.org
Cc: netdev@...r.kernel.org, 
 Krzysztof Galazka <krzysztof.galazka@...el.com>, 
 Przemek Kitszel <przemyslaw.kitszel@...el.com>
Subject: Re: [PATCH iwl-net] selftests/net: Fix csum test for short packets

Krzysztof Galazka wrote:
> For IPv4 and IPv6 packets shorter than minimum Ethernet
> frame payload, recvmsg returns lenght including padding.

nit: length

> Use length from header for checksum verification to avoid
> csum test failing on correct packets.
> 
> Fixes: 1d0dc857b5d8 (selftests: drv-net: add checksum tests)
> Signed-off-by: Krzysztof Galazka <krzysztof.galazka@...el.com>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>

This is not Intel driver specific, so can be sent straight to net

> ---
>  tools/testing/selftests/net/lib/csum.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/lib/csum.c b/tools/testing/selftests/net/lib/csum.c
> index b9f3fc3c3426..3dbaf2ecd59e 100644
> --- a/tools/testing/selftests/net/lib/csum.c
> +++ b/tools/testing/selftests/net/lib/csum.c
> @@ -658,6 +658,9 @@ static int recv_verify_packet_ipv4(void *nh, int len)
>  	if (len < sizeof(*iph) || iph->protocol != proto)
>  		return -1;
>  
> +	/* For short packets recvmsg returns length with padding, fix that */
> +	len = ntohs(iph->tot_len);
> +

Are you running into this while running the standard testsuite in
csum.py, or a specific custom invocation?

Since the checksum is an L3 feature, trusting the L3 length field for
this makes sense (as long as the packet wasn't truncated).

>  	iph_addr_p = &iph->saddr;
>  	if (proto == IPPROTO_TCP)
>  		return recv_verify_packet_tcp(iph + 1, len - sizeof(*iph));
> @@ -673,6 +676,9 @@ static int recv_verify_packet_ipv6(void *nh, int len)
>  	if (len < sizeof(*ip6h) || ip6h->nexthdr != proto)
>  		return -1;
>  
> +	/* For short packets recvmsg returns length with padding, fix that */
> +	len = sizeof(*ip6h) + ntohs(ip6h->payload_len);
> +
>  	iph_addr_p = &ip6h->saddr;
>  
>  	if (proto == IPPROTO_TCP)
> -- 
> 2.43.0
>