From: Eric Dumazet Date: Fri, 11 Apr 2014 04:23:36 +0000 (-0700) Subject: ipv6: Limit mtu to 65575 bytes X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=30f78d8ebf7f514801e71b88a10c948275168518;p=linux-beck.git ipv6: Limit mtu to 65575 bytes Francois reported that setting big mtu on loopback device could prevent tcp sessions making progress. We do not support (yet ?) IPv6 Jumbograms and cook corrupted packets. We must limit the IPv6 MTU to (65535 + 40) bytes in theory. Tested: ifconfig lo mtu 70000 netperf -H ::1 Before patch : Throughput : 0.05 Mbits After patch : Throughput : 35484 Mbits Reported-by: Francois WELLENREITER Signed-off-by: Eric Dumazet Acked-by: YOSHIFUJI Hideaki Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h index 3c3bb184eb8f..6c4f5eac98e7 100644 --- a/include/net/ip6_route.h +++ b/include/net/ip6_route.h @@ -32,6 +32,11 @@ struct route_info { #define RT6_LOOKUP_F_SRCPREF_PUBLIC 0x00000010 #define RT6_LOOKUP_F_SRCPREF_COA 0x00000020 +/* We do not (yet ?) support IPv6 jumbograms (RFC 2675) + * Unlike IPv4, hdr->seg_len doesn't include the IPv6 header + */ +#define IP6_MAX_MTU (0xFFFF + sizeof(struct ipv6hdr)) + /* * rt6_srcprefs2flags() and rt6_flags2srcprefs() translate * between IPV6_ADDR_PREFERENCES socket option values diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 5015c50a5ba7..5ea462eacd9f 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1338,7 +1338,7 @@ static unsigned int ip6_mtu(const struct dst_entry *dst) unsigned int mtu = dst_metric_raw(dst, RTAX_MTU); if (mtu) - return mtu; + goto out; mtu = IPV6_MIN_MTU; @@ -1348,7 +1348,8 @@ static unsigned int ip6_mtu(const struct dst_entry *dst) mtu = idev->cnf.mtu6; rcu_read_unlock(); - return mtu; +out: + return min_t(unsigned int, mtu, IP6_MAX_MTU); } static struct dst_entry *icmp6_dst_gc_list;