From: Maciej Żenczykowski <maze@google.com> [ Upstream commit 09454fd0a4ce23cb3d8af65066c91a1bf27120dd ] This reverts commit 19bda36c4299ce3d7e5bce10bebe01764a655a6d: | ipv6: add mtu lock check in __ip6_rt_update_pmtu | | Prior to this patch, ipv6 didn't do mtu lock check in ip6_update_pmtu. | It leaded to that mtu lock doesn't really work when receiving the pkt | of ICMPV6_PKT_TOOBIG. | | This patch is to add mtu lock check in __ip6_rt_update_pmtu just as ipv4 | did in __ip_rt_update_pmtu. The above reasoning is incorrect. IPv6 *requires* icmp based pmtu to work. There's already a comment to this effect elsewhere in the kernel: $ git grep -p -B1 -A3 'RTAX_MTU lock' net/ipv6/route.c=4813= static int rt6_mtu_change_route(struct fib6_info *f6i, void *p_arg) ... /* In IPv6 pmtu discovery is not optional, so that RTAX_MTU lock cannot disable it. We still use this lock to block changes caused by addrconf/ndisc. */ This reverts to the pre-4.9 behaviour. Cc: Eric Dumazet <edumazet@google.com> Cc: Willem de Bruijn <willemb@google.com> Cc: Xin Long <lucien.xin@gmail.com> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: Maciej Żenczykowski <maze@google.com> Fixes: 19bda36c4299 ("ipv6: add mtu lock check in __ip6_rt_update_pmtu") Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- net/ipv6/route.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index d0763bc..84be9b4 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -2360,8 +2360,10 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk, const struct in6_addr *daddr, *saddr; struct rt6_info *rt6 = (struct rt6_info *)dst; - if (dst_metric_locked(dst, RTAX_MTU)) - return; + /* Note: do *NOT* check dst_metric_locked(dst, RTAX_MTU) + * IPv6 pmtu discovery isn't optional, so 'mtu lock' cannot disable it. + * [see also comment in rt6_mtu_change_route()] + */ if (iph) { daddr = &iph->daddr; -- 1.8.3