netdev - [PATCH net] ipv4: fix route update on metric change.

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Message-Id: <84623b02bd882d91555b9bf76ea58d6cff29cd2a.1571908701.git.pabeni@redhat.com>
Date:   Thu, 24 Oct 2019 11:19:49 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     David Ahern <dsahern@...il.com>,
        Beniamino Galvani <bgalvani@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH net] ipv4: fix route update on metric change.

Since commit af4d768ad28c ("net/ipv4: Add support for specifying metric
of connected routes"), when updating an IP address with a different metric,
the associated connected route is updated, too.

Still, the mentioned commit doesn't handle properly some corner cases:

$ ip addr add dev eth0 192.168.1.0/24
$ ip addr add dev eth0 192.168.2.1/32 peer 192.168.2.2
$ ip addr add dev eth0 192.168.3.1/24
$ ip addr change dev eth0 192.168.1.0/24 metric 10
$ ip addr change dev eth0 192.168.2.1/32 peer 192.168.2.2 metric 10
$ ip addr change dev eth0 192.168.3.1/24 metric 10
$ ip -4 route
192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.0
192.168.2.2 dev eth0 proto kernel scope link src 192.168.2.1
192.168.3.0/24 dev eth0 proto kernel scope link src 192.168.2.1 metric 10

Only the last route is correctly updated.

The problem is the current test in fib_modify_prefix_metric():

	if (!(dev->flags & IFF_UP) ||
	    ifa->ifa_flags & (IFA_F_SECONDARY | IFA_F_NOPREFIXROUTE) ||
	    ipv4_is_zeronet(prefix) ||
	    prefix == ifa->ifa_local || ifa->ifa_prefixlen == 32)

Which should be the logical 'not' of the pre-existing test in
fib_add_ifaddr():

	if (!ipv4_is_zeronet(prefix) && !(ifa->ifa_flags & IFA_F_SECONDARY) &&
	    (prefix != addr || ifa->ifa_prefixlen < 32))

To properly negate the original expression, we need to change the last
logical 'or' to a logical 'and'.

Fixes: af4d768ad28c ("net/ipv4: Add support for specifying metric of connected routes")
Reported-and-suggested-by: Beniamino Galvani <bgalvani@...hat.com>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/ipv4/fib_frontend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index dde77f72e03e..71c78d223dfd 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1148,7 +1148,7 @@ void fib_modify_prefix_metric(struct in_ifaddr *ifa, u32 new_metric)
 	if (!(dev->flags & IFF_UP) ||
 	    ifa->ifa_flags & (IFA_F_SECONDARY | IFA_F_NOPREFIXROUTE) ||
 	    ipv4_is_zeronet(prefix) ||
-	    prefix == ifa->ifa_local || ifa->ifa_prefixlen == 32)
+	    (prefix == ifa->ifa_local && ifa->ifa_prefixlen == 32))
 		return;
 
 	/* add the new */
-- 
2.21.0