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>

1 files changed, 15 insertions, 6 deletions

diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
index 8ce904786116..4bf28f25f368 100644
--- 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;
         }