Patch "route: check sysctl_fib_multipath_use_neigh earlier than hash" has been added to the 4.9-stable tree

Patch "route: check sysctl_fib_multipath_use_neigh earlier than hash" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    route: check sysctl_fib_multipath_use_neigh earlier than hash

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     route-check-sysctl_fib_multipath_use_neigh-earlier-than-hash.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Apr 11 10:26:56 CEST 2018
From: Xin Long <lucien.xin@gmail.com>
Date: Sun, 1 Apr 2018 22:40:35 +0800
Subject: route: check sysctl_fib_multipath_use_neigh earlier than hash

From: Xin Long <lucien.xin@gmail.com>


[ Upstream commit 6174a30df1b902e1fedbd728f5343937e83e64e6 ]

Prior to this patch, when one packet is hashed into path [1]
(hash <= nh_upper_bound) and it's neigh is dead, it will try
path [2]. However, if path [2]'s neigh is alive but it's
hash > nh_upper_bound, it will not return this alive path.
This packet will never be sent even if path [2] is alive.

 3.3.3.1/24:
  nexthop via 1.1.1.254 dev eth1 weight 1 <--[1] (dead neigh)
  nexthop via 2.2.2.254 dev eth2 weight 1 <--[2]

With sysctl_fib_multipath_use_neigh set is supposed to find an
available path respecting to the l3/l4 hash. But if there is
no available route with this hash, it should at least return
an alive route even with other hash.

This patch is to fix it by processing fib_multipath_use_neigh
earlier than the hash check, so that it will at least return
an alive route if there is when fib_multipath_use_neigh is
enabled. It's also compatible with before when there are alive
routes with the l3/l4 hash.

Fixes: a6db4494d218 ("net: ipv4: Consider failed nexthops in multipath routes")
Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/fib_semantics.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1611,18 +1611,20 @@ void fib_select_multipath(struct fib_res
 	bool first = false;
 
 	for_nexthops(fi) {
+		if (net->ipv4.sysctl_fib_multipath_use_neigh) {
+			if (!fib_good_nh(nh))
+				continue;
+			if (!first) {
+				res->nh_sel = nhsel;
+				first = true;
+			}
+		}
+
 		if (hash > atomic_read(&nh->nh_upper_bound))
 			continue;
 
-		if (!net->ipv4.sysctl_fib_multipath_use_neigh ||
-		    fib_good_nh(nh)) {
-			res->nh_sel = nhsel;
-			return;
-		}
-		if (!first) {
-			res->nh_sel = nhsel;
-			first = true;
-		}
+		res->nh_sel = nhsel;
+		return;
 	} endfor_nexthops(fi);
 }
 #endif


Patches currently in stable-queue which might be from lucien.xin@gmail.com are

queue-4.9/team-move-dev_mc_sync-after-master_upper_dev_link-in-team_port_add.patch
queue-4.9/bonding-process-the-err-returned-by-dev_set_allmulti-properly-in-bond_enslave.patch
queue-4.9/bonding-fix-the-err-path-for-dev-hwaddr-sync-in-bond_enslave.patch
queue-4.9/bonding-move-dev_mc_sync-after-master_upper_dev_link-in-bond_enslave.patch
queue-4.9/route-check-sysctl_fib_multipath_use_neigh-earlier-than-hash.patch
queue-4.9/sctp-fix-recursive-locking-warning-in-sctp_do_peeloff.patch