diff options
authorEric Dumazet <edumazet@google.com>2012-05-18 11:02:15 +0000
committerDavid S. Miller <davem@davemloft.net>2012-05-18 23:49:33 -0400
commit72e843bb09d4533208aa5573861a983c46914019 (patch)
parent6fba180ee8b1c86b03d33013b4c2fc54fc5fc248 (diff)
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>
1 files changed, 4 insertions, 0 deletions
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index a254e4b5d968..3dc633f39372 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -788,6 +788,10 @@ slow_path_clean:
+ if ((skb->ip_summed == CHECKSUM_PARTIAL) &&
+ skb_checksum_help(skb))
+ goto fail;
left = skb->len - hlen; /* Space per frame */
ptr = hlen; /* Where to start from */

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