neighbour: Namespacify neigh_tables.

Now, neigh_table is ready to be namespacified.

Let's allocate per-netns neigh_table in neigh_table_register()
and call neigh_table_init() and neigh_sysctl_register() for it.

proc_create_seq_data() is changed to proc_create_net_data().

Since each netns has its own sysctl knobs, RTM_SETNEIGHTBL can
configure the default table param (ifindex==0) and GC parameters
per netns.

To avoid potential regression, all the default parameters under
/proc/sys/net/ipv{4,6}/neigh/default/, are inherited from init_net
by default.

This behaviour is controlled by a new sysctl knob,
net.core.neigh_inherit_init_net:

  # sysctl net.core.neigh_inherit_init_net
  net.core.neigh_inherit_init_net = 1
  # sysctl net.ipv4.neigh.default.gc_thresh1
  net.ipv4.neigh.default.gc_thresh1 = 128
  # sysctl net.ipv4.neigh.default.gc_thresh1=129
  net.ipv4.neigh.default.gc_thresh1 = 129
  # unshare -n sysctl net.ipv4.neigh.default.gc_thresh1
  net.ipv4.neigh.default.gc_thresh1 = 129

If it is turned off, all settings are reset in the new netns:

  # sysctl net.core.neigh_inherit_init_net=0
  net.core.neigh_inherit_init_net = 0
  # unshare -n sysctl net.ipv4.neigh.default.gc_thresh1
  net.ipv4.neigh.default.gc_thresh1 = 128

The next patch will remove other unnecessary net_eq().

Note that CONFIG_SYSCTL cannot be enabled without CONFIG_PROC_FS.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260902203722.926528-13-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index e586e17fc7a5..fe43e8595958 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -413,6 +413,20 @@ new netns has been created.
 
 Default : 0  (for compatibility reasons)
 
+neigh_inherit_init_net
+----------------------
+
+Controls if a new network namespace should inherit all current
+settings under /proc/sys/net/ipv{4,6}/neigh/default/.
+
+By default, the value is set to 1, and all settings are inherited
+from init_net.
+
+If set to 0, both IPv4 and IPv6 settings are reset to their default
+values.
+
+Default : 1  (for compatibility reasons)
+
 txrehash
 --------