net: Fix IP_MULTICAST_IF

ipv4/ipv6 setsockopt(IP_MULTICAST_IF) have dubious __dev_get_by_index() calls.

This function should be called only with RTNL or dev_base_lock held, or reader
could see a corrupt hash chain and eventually enter an endless loop.

Fix is to call dev_get_by_index()/dev_put().

If this happens to be performance critical, we could define a new dev_exist_by_index()
function to avoid touching dev refcount.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 4 deletions

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 0c0b6e363a20..e982b5c1ee17 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -634,17 +634,16 @@ static int do_ip_setsockopt(struct sock *sk, int level,
                                 break;
                         }
                         dev = ip_dev_find(sock_net(sk), mreq.imr_address.s_addr);
-                        if (dev) {
+                        if (dev)
                                 mreq.imr_ifindex = dev->ifindex;
-                                dev_put(dev);
-                        }
                 } else
-                        dev = __dev_get_by_index(sock_net(sk), mreq.imr_ifindex);
+                        dev = dev_get_by_index(sock_net(sk), mreq.imr_ifindex);
 
 
                 err = -EADDRNOTAVAIL;
                 if (!dev)
                         break;
+                dev_put(dev);
 
                 err = -EINVAL;
                 if (sk->sk_bound_dev_if &&