Commit d96016a7 authored Oct 11, 2024 by Jakub Sitnicki Committed by Jakub Kicinski Oct 15, 2024

udp: Compute L4 checksum as usual when not segmenting the skb



If:

  1) the user requested USO, but
  2) there is not enough payload for GSO to kick in, and
  3) the egress device doesn't offer checksum offload, then

we want to compute the L4 checksum in software early on.

In the case when we are not taking the GSO path, but it has been requested,
the software checksum fallback in skb_segment doesn't get a chance to
compute the full checksum, if the egress device can't do it. As a result we
end up sending UDP datagrams with only a partial checksum filled in, which
the peer will discard.

Fixes: 10154dbd ("udp: Allow GSO transmit from devices with no checksum offload")
Reported-by: Ivan Babrou <ivan@cloudflare.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20241011-uso-swcsum-fixup-v2-1-6e1ddc199af9@cloudflare.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

parent 56440d7e

net/ipv4/udp.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -951,9 +951,11 @@ static int udp_send_skb(struct sk_buff skb, struct flowi4 fl4,
		skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
		cork->gso_size);
		}

		/* Don't checksum the payload, skb will get segmented */
		goto csum_partial;
		}
		}

		if (is_udplite) /* UDP-Lite */
		csum = udplite_csum(skb);

net/ipv6/udp.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -1266,9 +1266,11 @@ static int udp_v6_send_skb(struct sk_buff skb, struct flowi6 fl6,
		skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
		cork->gso_size);
		}

		/* Don't checksum the payload, skb will get segmented */
		goto csum_partial;
		}
		}

		if (is_udplite)
		csum = udplite_csum(skb);