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

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Message-ID: <0c0f51d5-8ff1-44f5-8607-cee88479aa62@intel.com>
Date: Tue, 27 Aug 2024 19:54:37 +0200
From: "Galazka, Krzysztof" <krzysztof.galazka@...el.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
CC: <netdev@...r.kernel.org>, Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	<intel-wired-lan@...ts.osuosl.org>
Subject: Re: [PATCH iwl-net] selftests/net: Fix csum test for short packets



On 2024-08-21 16:32, Willem de Bruijn wrote:
> 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?

It was with standard testsuite in csum.py. Not on every run but quite often.

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

Ah, I haven't thought about truncated packets. I'll add condition to 
update length returned by recvmsg only if it's greater then expected.


Thanks,
Krzysiek