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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.

Fixes: f6fb8f1 ("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>
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ltspp-test authored and davem330 committed Nov 30, 2016
1 parent 2219d5e commit 84ac7260236a49c79eede91617700174c2c19b0c
Showing with 12 additions and 6 deletions.
  1. +12 −6 net/packet/af_packet.c
@@ -3648,19 +3648,25 @@ 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:
case TPACKET_V3:
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:
{
@@ -4164,6 +4170,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
/* Added to avoid minimal code churn */
struct tpacket_req *req = &req_u->req;

lock_sock(sk);
/* Opening a Tx-ring is NOT supported in TPACKET_V3 */
if (!closing && tx_ring && (po->tp_version > TPACKET_V2)) {
net_warn_ratelimited("Tx-ring is not supported.\n");
@@ -4245,7 +4252,6 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
goto out;
}

lock_sock(sk);

/* Detach socket from network */
spin_lock(&po->bind_lock);
@@ -4294,11 +4300,11 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
if (!tx_ring)
prb_shutdown_retire_blk_timer(po, rb_queue);
}
release_sock(sk);

if (pg_vec)
free_pg_vec(pg_vec, order, req->tp_block_nr);
out:
release_sock(sk);
return err;
}

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