packet: fix race condition in packet_set_ring

When packet_set_ring creates a ring buffer it will initialize a
struct timer_list if the packet version is TPACKET_V3. This value
can then be raced by a different thread calling setsockopt to
set the version to TPACKET_V1 before packet_set_ring has finished.

This leads to a use-after-free on a function pointer in the
struct timer_list when the socket is closed as the previously
initialized timer will not be deleted.

The bug is fixed by taking lock_sock(sk) in packet_setsockopt when
changing the packet version while also taking the lock at the start
of packet_set_ring.

Change-Id: Iec8b20f499134e1edd0f9214aa4dde477d1674e1
Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
Signed-off-by: Philip Pettersson <philip.pettersson@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 8 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d596ceb967f..d0c3cd7dd12 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2014,18 +2014,24 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 
 		if (optlen != sizeof(val))
 			return -EINVAL;
-		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)
-			return -EBUSY;
 		if (copy_from_user(&val, optval, sizeof(val)))
 			return -EFAULT;
 		switch (val) {
 		case TPACKET_V1:
 		case TPACKET_V2:
-			po->tp_version = val;
-			return 0;
+			break;
 		default:
 			return -EINVAL;
 		}
+		lock_sock(sk);
+		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
+			ret = -EBUSY;
+		} else {
+			po->tp_version = val;
+			ret = 0;
+		}
+		release_sock(sk);
+		return ret;
 	}
 	case PACKET_RESERVE:
 	{
@@ -2463,6 +2469,8 @@ static int packet_set_ring(struct sock *sk, struct tpacket_req *req,
 	rb = tx_ring ? &po->tx_ring : &po->rx_ring;
 	rb_queue = tx_ring ? &sk->sk_write_queue : &sk->sk_receive_queue;
 
+	lock_sock(sk);
+
 	err = -EBUSY;
 	if (!closing) {
 		if (atomic_read(&po->mapped))
@@ -2517,8 +2525,6 @@ static int packet_set_ring(struct sock *sk, struct tpacket_req *req,
 			goto out;
 	}
 
-	lock_sock(sk);
-
 	/* Detach socket from network */
 	spin_lock(&po->bind_lock);
 	was_running = po->running;
@@ -2566,11 +2572,10 @@ static int packet_set_ring(struct sock *sk, struct tpacket_req *req,
 	}
 	spin_unlock(&po->bind_lock);
 
-	release_sock(sk);
-
 	if (pg_vec)
 		free_pg_vec(pg_vec, order, req->tp_block_nr);
 out:
+	release_sock(sk);
 	return err;
 }