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    Subject[PATCH 3.16 191/294] packet: in packet_do_bind, test fanout with bind_lock held
    3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Willem de Bruijn <willemb@google.com>

    commit 4971613c1639d8e5f102c4e797c3bf8f83a5a69e upstream.

    Once a socket has po->fanout set, it remains a member of the group
    until it is destroyed. The prot_hook must be constant and identical
    across sockets in the group.

    If fanout_add races with packet_do_bind between the test of po->fanout
    and taking the lock, the bind call may make type or dev inconsistent
    with that of the fanout group.

    Hold po->bind_lock when testing po->fanout to avoid this race.

    I had to introduce artificial delay (local_bh_enable) to actually
    observe the race.

    Fixes: dc99f600698d ("packet: Add fanout support.")
    Signed-off-by: Willem de Bruijn <willemb@google.com>
    Reviewed-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 | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    --- a/net/packet/af_packet.c
    +++ b/net/packet/af_packet.c
    @@ -2696,13 +2696,15 @@ static int packet_do_bind(struct sock *s
    int ret = 0;
    bool unlisted = false;

    - if (po->fanout)
    - return -EINVAL;
    -
    lock_sock(sk);
    spin_lock(&po->bind_lock);
    rcu_read_lock();

    + if (po->fanout) {
    + ret = -EINVAL;
    + goto out_unlock;
    + }
    +
    if (name) {
    dev = dev_get_by_name_rcu(sock_net(sk), name);
    if (!dev) {
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