net: Fix sysctl restarts...

Yuck.  It turns out that when we restart sysctls we were restarting
with the values already changed.  Which unfortunately meant that
the second time through we thought there was no change and skipped
all kinds of work, despite the fact that there was indeed a change.

I have fixed this the simplest way possible by restoring the changed
values when we restart the sysctl write.

One of my coworkers spotted this bug when after disabling forwarding
on an interface pings were still forwarded.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 040c4f05b653..26dec2be9615 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1317,14 +1317,19 @@ static int devinet_sysctl_forward(ctl_table *ctl, int write,
 {
         int *valp = ctl->data;
         int val = *valp;
+        loff_t pos = *ppos;
         int ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
 
         if (write && *valp != val) {
                 struct net *net = ctl->extra2;
 
                 if (valp != &IPV4_DEVCONF_DFLT(net, FORWARDING)) {
-                        if (!rtnl_trylock())
+                        if (!rtnl_trylock()) {
+                                /* Restore the original values before restarting */
+                                *valp = val;
+                                *ppos = pos;
                                 return restart_syscall();
+                        }
                         if (valp == &IPV4_DEVCONF_ALL(net, FORWARDING)) {
                                 inet_forward_change(net);
                         } else if (*valp) {