net: Fix devinet_sysctl_forward

sysctls are unregistered with the rntl_lock held making
it unsafe to unconditionally grab the the rtnl_lock.  Instead
we need to call rtnl_trylock and restart the system call
if we can not grab it.  Otherwise we could deadlock at unregistration
time.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 126bb911880f..3863c3a4223f 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1347,7 +1347,8 @@ static int devinet_sysctl_forward(ctl_table *ctl, int write,
                 struct net *net = ctl->extra2;
 
                 if (valp != &IPV4_DEVCONF_DFLT(net, FORWARDING)) {
-                        rtnl_lock();
+                        if (!rtnl_trylock())
+                                return restart_syscall();
                         if (valp == &IPV4_DEVCONF_ALL(net, FORWARDING)) {
                                 inet_forward_change(net);
                         } else if (*valp) {