ipv4: enable route flushing in network namespaces

Tools such as vpnc try to flush routes when run inside network
namespaces by writing 1 into /proc/sys/net/ipv4/route/flush. This
currently does not work because flush is not enabled in non-initial
network namespaces.
Since routes are per network namespace it is safe to enable
/proc/sys/net/ipv4/route/flush in there.

Link: https://github.com/lxc/lxd/issues/4257
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index a3e466b..bbd55c7 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -3326,9 +3326,11 @@ static struct ctl_table ipv4_route_table[] = {
        { }
 };
 
+static const char ipv4_route_flush_procname[] = "flush";
+
 static struct ctl_table ipv4_route_flush_table[] = {
        {
-               .procname       = "flush",
+               .procname       = ipv4_route_flush_procname,
                .maxlen         = sizeof(int),
                .mode           = 0200,
                .proc_handler   = ipv4_sysctl_rtcache_flush,
@@ -3346,9 +3348,11 @@ static __net_init int sysctl_route_net_init(struct net *net)
                if (!tbl)
                        goto err_dup;
 
-               /* Don't export sysctls to unprivileged users */
-               if (net->user_ns != &init_user_ns)
-                       tbl[0].procname = NULL;
+               /* Don't export non-whitelisted sysctls to unprivileged users */
+               if (net->user_ns != &init_user_ns) {
+                       if (tbl[0].procname != ipv4_route_flush_procname)
+                               tbl[0].procname = NULL;
+               }
        }
        tbl[0].extra1 = net;