net/ipv6: avoid possible dead locking on addr_gen_mode sysctl

The addr_gen_mode variable can be accessed by both sysctl and netlink.
Repleacd rtnl_lock() with rtnl_trylock() protect the sysctl operation to
avoid the possbile dead lock.`

Signed-off-by: Felix Jia <felix.jia@alliedtelesis.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 7 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3a2025f5bf2c..cfc485a8e1c0 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5692,13 +5692,18 @@ static int addrconf_sysctl_addr_gen_mode(struct ctl_table *ctl, int write,
         struct inet6_dev *idev = (struct inet6_dev *)ctl->extra1;
         struct net *net = (struct net *)ctl->extra2;
 
+        if (!rtnl_trylock())
+                return restart_syscall();
+
         ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
 
         if (write) {
                 new_val = *((int *)ctl->data);
 
-                if (check_addr_gen_mode(new_val) < 0)
-                        return -EINVAL;
+                if (check_addr_gen_mode(new_val) < 0) {
+                        ret = -EINVAL;
+                        goto out;
+                }
 
                 /* request for default */
                 if (&net->ipv6.devconf_dflt->addr_gen_mode == ctl->data) {
@@ -5707,20 +5712,23 @@ static int addrconf_sysctl_addr_gen_mode(struct ctl_table *ctl, int write,
                 /* request for individual net device */
                 } else {
                         if (!idev)
-                                return ret;
+                                goto out;
 
-                        if (check_stable_privacy(idev, net, new_val) < 0)
-                                return -EINVAL;
+                        if (check_stable_privacy(idev, net, new_val) < 0) {
+                                ret = -EINVAL;
+                                goto out;
+                        }
 
                         if (idev->cnf.addr_gen_mode != new_val) {
                                 idev->cnf.addr_gen_mode = new_val;
-                                rtnl_lock();
                                 addrconf_dev_config(idev->dev);
-                                rtnl_unlock();
                         }
                 }
         }
 
+out:
+        rtnl_unlock();
+
         return ret;
 }