[PATCH 3.16 271/306] packet: fix race condition in packet_set_ring

Ben Hutchings
2017-02-15T23:12:42Z

From: Philip Pettersson <philip.pettersson@gmail.com>

commit 84ac7260236a49c79eede91617700174c2c19b0c upstream.

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: 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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/packet/af_packet.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3304,19 +3304,25 @@ packet_setsockopt(struct socket *sock, i

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:
{
@@ -3779,6 +3785,7 @@ static int packet_set_ring(struct sock *
/* 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)) {
WARN(1, "Tx-ring is not supported.\n");
@@ -3860,7 +3867,6 @@ static int packet_set_ring(struct sock *
goto out;
}

- lock_sock(sk);

/* Detach socket from network */
spin_lock(&po->bind_lock);
@@ -3909,11 +3915,11 @@ static int packet_set_ring(struct sock *
if (!tx_ring)
prb_shutdown_retire_blk_timer(po, tx_ring, rb_queue);
}
- release_sock(sk);

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