netdev - Re: [PATCH net] udp: fix receiving fraglist GSO packets

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Message-ID: <66c3a2be81834_740b1294db@willemb.c.googlers.com.notmuch>
Date: Mon, 19 Aug 2024 15:53:34 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Felix Fietkau <nbd@....name>, 
 netdev@...r.kernel.org, 
 "David S. Miller" <davem@...emloft.net>, 
 David Ahern <dsahern@...nel.org>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Willem de Bruijn <willemb@...gle.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] udp: fix receiving fraglist GSO packets

Felix Fietkau wrote:
> When assembling fraglist GSO packets, udp4_gro_complete does not set
> skb->csum_start, which makes the extra validation in __udp_gso_segment fail.
> 
> Fixes: 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr")
> Signed-off-by: Felix Fietkau <nbd@....name>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>

Oh right, UDP GRO fraglist skbs are converted to CHECKSUM_UNNECSSARY
with __skb_incr_checksum_unnecessary.

Rather than to CHECKSUM_PARTIAL, as udp_gro_complete_segment does for
non fraglist GRO packets.

virtio_net_hdr_to_skb cannot generate fraglist packets, so this bad
input check is unnecessary for SKB_GSO_FRAGLIST too.

Thanks for the fix, Felix.