net ipv6: Fix duplicate /proc/sys/net/ipv6/neigh directory entries.

When I was fixing issues with unregisgtering tables under /proc/sys/net/ipv6/neigh
by adding a mount point it appears I missed a critical ordering issue, in the
ipv6 initialization.  I had not realized that ipv6_sysctl_register is called
at the very end of the ipv6 initialization and in particular after we call
neigh_sysctl_register from ndisc_init.

"neigh" needs to be initialized in ipv6_static_sysctl_register which is
the first ipv6 table to initialized, and definitely before ndisc_init.
This removes the weirdness of duplicate tables while still providing a
"neigh" mount point which prevents races in sysctl unregistering.

This was initially reported at https://bugzilla.kernel.org/show_bug.cgi?id=31232
Reported-by: sunkan@zappa.cx
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 7 deletions

diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index 7cb65ef79f9c..6dcf5e7d661b 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -17,6 +17,16 @@
 
 static struct ctl_table empty[1];
 
+static ctl_table ipv6_static_skeleton[] = {
+        {
+                .procname       = "neigh",
+                .maxlen         = 0,
+                .mode           = 0555,
+                .child          = empty,
+        },
+        { }
+};
+
 static ctl_table ipv6_table_template[] = {
         {
                 .procname       = "route",
@@ -37,12 +47,6 @@ static ctl_table ipv6_table_template[] = {
                 .mode           = 0644,
                 .proc_handler   = proc_dointvec
         },
-        {
-                .procname       = "neigh",
-                .maxlen         = 0,
-                .mode           = 0555,
-                .child          = empty,
-        },
         { }
 };
 
@@ -160,7 +164,7 @@ static struct ctl_table_header *ip6_base;
 
 int ipv6_static_sysctl_register(void)
 {
-        ip6_base = register_sysctl_paths(net_ipv6_ctl_path, empty);
+        ip6_base = register_sysctl_paths(net_ipv6_ctl_path, ipv6_static_skeleton);
         if (ip6_base == NULL)
                 return -ENOMEM;
         return 0;