ipv6: ip6_fragment() should check CHECKSUM_PARTIAL
Quoting Tore Anderson from : If the allfrag feature has been set on a host route (due to an ICMPv6 Packet Too Big received indicating a MTU of less than 1280), TCP SYN/ACK packets to that destination appears to get an incorrect TCP checksum. This in turn means they are thrown away as invalid. In the case of an IPv4 client behind a link with a MTU of less than 1260, accessing an IPv6 server through a stateless translator, this means that the client can only download a single large file from the server, because once it is in the server's routing cache with the allfrag feature set, new TCP connections can no longer be established. </endquote> It appears ip6_fragment() doesn't handle CHECKSUM_PARTIAL properly. As network drivers are not prepared to fetch correct transport header, a safe fix is to call skb_checksum_help() before fragmenting packet. Reported-by: Tore Anderson <tore@fud.no> Signed-off-by: Eric Dumazet <edumazet@google.com> Tested-by: Tore Anderson <tore@fud.no> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -788,6 +788,10 @@ slow_path_clean:
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}
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slow_path:
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if ((skb->ip_summed == CHECKSUM_PARTIAL) &&
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skb_checksum_help(skb))
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goto fail;
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left = skb->len - hlen; /* Space per frame */
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ptr = hlen; /* Where to start from */
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