netdev - [PATCH] net: ipv4: fix multipath RTM_GETROUTE behavior when iif is given

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Message-Id: <20170403144609.18716-1-fl@n621.de>
Date:   Mon,  3 Apr 2017 16:46:09 +0200
From:   Florian Larysch <fl@...1.de>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Florian Larysch <fl@...1.de>
Subject: [PATCH] net: ipv4: fix multipath RTM_GETROUTE behavior when iif is given

inet_rtm_getroute synthesizes a skeletal ICMP skb, which is passed to
ip_route_input when iif is given. If a multipath route is present for
the designated destination, ip_multipath_icmp_hash ends up being called,
which uses the source/destination addresses within the skb to calculate
a hash. However, those are not set in the synthetic skb, causing it to
return an arbitrary and incorrect result.

Instead, use UDP, which gets no such special treatment.

Signed-off-by: Florian Larysch <fl@...1.de>
---
 net/ipv4/route.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8471dd116771..acd69cfe2951 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2620,7 +2620,7 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh)
 	skb_reset_network_header(skb);

 	/* Bugfix: need to give ip_route_input enough of an IP header to not gag. */
-	ip_hdr(skb)->protocol = IPPROTO_ICMP;
+	ip_hdr(skb)->protocol = IPPROTO_UDP;
 	skb_reserve(skb, MAX_HEADER + sizeof(struct iphdr));

 	src = tb[RTA_SRC] ? nla_get_in_addr(tb[RTA_SRC]) : 0;
-- 
2.12.0