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    Subject[PATCH 3.2 096/126] packet: fix race condition in packet_set_ring
    3.2.85-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    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
    @@ -3077,19 +3077,25 @@ 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:
    {
    @@ -3560,6 +3566,7 @@ 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");
    @@ -3637,7 +3644,6 @@ static int packet_set_ring(struct sock *
    goto out;
    }

    - lock_sock(sk);

    /* Detach socket from network */
    spin_lock(&po->bind_lock);
    @@ -3686,11 +3692,11 @@ 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;
    }

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