net: arp_ioctl() must hold RTNL

Commit 941666c2e3e0 "net: RCU conversion of dev_getbyhwaddr() and
arp_ioctl()" introduced a regression, reported by Jamie Heilman.
"arp -Ds 192.168.2.41 eth0 pub" triggered the ASSERT_RTNL() assert
in pneigh_lookup()

Removing RTNL requirement from arp_ioctl() was a mistake, just revert
that part.

Reported-by: Jamie Heilman <jamie@audible.transient.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 6 deletions

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 04c8b69fd426..7927589813b5 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1017,14 +1017,13 @@ static int arp_req_set_proxy(struct net *net, struct net_device *dev, int on)
                 IPV4_DEVCONF_ALL(net, PROXY_ARP) = on;
                 return 0;
         }
-        if (__in_dev_get_rcu(dev)) {
-                IN_DEV_CONF_SET(__in_dev_get_rcu(dev), PROXY_ARP, on);
+        if (__in_dev_get_rtnl(dev)) {
+                IN_DEV_CONF_SET(__in_dev_get_rtnl(dev), PROXY_ARP, on);
                 return 0;
         }
         return -ENXIO;
 }
 
-/* must be called with rcu_read_lock() */
 static int arp_req_set_public(struct net *net, struct arpreq *r,
                 struct net_device *dev)
 {
@@ -1233,10 +1232,10 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
         if (!(r.arp_flags & ATF_NETMASK))
                 ((struct sockaddr_in *)&r.arp_netmask)->sin_addr.s_addr =
                                                            htonl(0xFFFFFFFFUL);
-        rcu_read_lock();
+        rtnl_lock();
         if (r.arp_dev[0]) {
                 err = -ENODEV;
-                dev = dev_get_by_name_rcu(net, r.arp_dev);
+                dev = __dev_get_by_name(net, r.arp_dev);
                 if (dev == NULL)
                         goto out;
 
@@ -1263,7 +1262,7 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
                 break;
         }
 out:
-        rcu_read_unlock();
+        rtnl_unlock();
         if (cmd == SIOCGARP && !err && copy_to_user(arg, &r, sizeof(r)))
                 err = -EFAULT;
         return err;