Commit a8c4a252 authored Feb 22, 2016 by Hannes Frederic Sowa Committed by David S. Miller Feb 24, 2016

ipv4: only create late gso-skb if skb is already set up with CHECKSUM_PARTIAL



Otherwise we break the contract with GSO to only pass CHECKSUM_PARTIAL
skbs down. This can easily happen with UDP+IPv4 sockets with the first
MSG_MORE write smaller than the MTU, second write is a sendfile.

Returning -EOPNOTSUPP lets the callers fall back into normal sendmsg path,
were we calculate the checksum manually during copying.

Commit d749c9cb ("ipv4: no CHECKSUM_PARTIAL on MSG_MORE corked
sockets") started to exposes this bug.

Fixes: d749c9cb ("ipv4: no CHECKSUM_PARTIAL on MSG_MORE corked sockets")
Reported-by: Jiri Benc <jbenc@redhat.com>
Cc: Jiri Benc <jbenc@redhat.com>
Reported-by: Wakko Warner <wakko@animx.eu.org>
Cc: Wakko Warner <wakko@animx.eu.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent c7dfe3ab

net/ipv4/ip_output.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -1236,13 +1236,16 @@ ssize_t ip_append_page(struct sock sk, struct flowi4 fl4, struct page *page,
		if (!skb)
		return -EINVAL;

		cork->length += size;
		if ((size + skb->len > mtu) &&
		(sk->sk_protocol == IPPROTO_UDP) &&
		(rt->dst.dev->features & NETIF_F_UFO)) {
		if (skb->ip_summed != CHECKSUM_PARTIAL)
		return -EOPNOTSUPP;

		skb_shinfo(skb)->gso_size = mtu - fragheaderlen;
		skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
		}
		cork->length += size;

		while (size > 0) {
		if (skb_is_gso(skb)) {

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