caif: fix two caif_connect() bugs

caif_connect() might dereference a netdevice after dev_put() it.

It also doesnt check dev_get_by_index() return value and could
dereference a NULL pointer.

Fix it, using RCU to avoid taking a reference.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Sjur Braendeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
index 8ce9047..4bf28f2 100644 (file)
--- a/net/caif/caif_socket.c
+++ b/net/caif/caif_socket.c
@@ -827,6 +827,7 @@ static int caif_connect(struct socket *sock, struct sockaddr *uaddr,
        long timeo;
        int err;
        int ifindex, headroom, tailroom;
+       unsigned int mtu;
        struct net_device *dev;
 
        lock_sock(sk);
@@ -896,15 +897,23 @@ static int caif_connect(struct socket *sock, struct sockaddr *uaddr,
                cf_sk->sk.sk_state = CAIF_DISCONNECTED;
                goto out;
        }
-       dev = dev_get_by_index(sock_net(sk), ifindex);
+
+       err = -ENODEV;
+       rcu_read_lock();
+       dev = dev_get_by_index_rcu(sock_net(sk), ifindex);
+       if (!dev) {
+               rcu_read_unlock();
+               goto out;
+       }
        cf_sk->headroom = LL_RESERVED_SPACE_EXTRA(dev, headroom);
+       mtu = dev->mtu;
+       rcu_read_unlock();
+
        cf_sk->tailroom = tailroom;
-       cf_sk->maxframe = dev->mtu - (headroom + tailroom);
-       dev_put(dev);
+       cf_sk->maxframe = mtu - (headroom + tailroom);
        if (cf_sk->maxframe < 1) {
-               pr_warning("CAIF: %s(): CAIF Interface MTU too small (%d)\n",
-                       __func__, dev->mtu);
-               err = -ENODEV;
+               pr_warning("CAIF: %s(): CAIF Interface MTU too small (%u)\n",
+                          __func__, mtu);
                goto out;
        }