Commit 09454fd0 authored May 05, 2020 by Maciej Żenczykowski Committed by David S. Miller May 07, 2020

Revert "ipv6: add mtu lock check in __ip6_rt_update_pmtu"



This reverts commit 19bda36c:

| 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: 19bda36c ("ipv6: add mtu lock check in __ip6_rt_update_pmtu")
Signed-off-by: David S. Miller <davem@davemloft.net>

parent ee287556

net/ipv6/route.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -2722,8 +2722,10 @@ 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;

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