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    Subject[PATCH] [31/139] llc: fix a device refcount imbalance
    Date
    2.6.35-longterm review patch.  If anyone has any objections, please let me know.

    ------------------
    From: Eric Dumazet <eric.dumazet@gmail.com>

    commit 35d9b0c906ad92d32a0b8db5daa6fabfcc2f068d upstream.

    Le dimanche 05 décembre 2010 à 12:23 +0100, Eric Dumazet a écrit :
    > Le dimanche 05 décembre 2010 à 09:19 +0100, Eric Dumazet a écrit :
    >
    > > Hmm..
    > >
    > > If somebody can explain why RTNL is held in arp_ioctl() (and therefore
    > > in arp_req_delete()), we might first remove RTNL use in arp_ioctl() so
    > > that your patch can be applied.
    > >
    > > Right now it is not good, because RTNL wont be necessarly held when you
    > > are going to call arp_invalidate() ?
    >
    > While doing this analysis, I found a refcount bug in llc, I'll send a
    > patch for net-2.6

    Oh well, of course I must first fix the bug in net-2.6, and wait David
    pull the fix in net-next-2.6 before sending this rcu conversion.

    Note: this patch should be sent to stable teams (2.6.34 and up)

    [PATCH net-2.6] llc: fix a device refcount imbalance

    commit abf9d537fea225 (llc: add support for SO_BINDTODEVICE) added one
    refcount imbalance in llc_ui_bind(), because dev_getbyhwaddr() doesnt
    take a reference on device, while dev_get_by_index() does.

    Fix this using RCU locking. And since an RCU conversion will be done for
    2.6.38 for dev_getbyhwaddr(), put the rcu_read_lock/unlock exactly at
    their final place.

    Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: Andi Kleen <ak@linux.intel.com>
    Cc: Octavian Purdila <opurdila@ixiacom.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    net/llc/af_llc.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    Index: linux-2.6.35.y/net/llc/af_llc.c
    ===================================================================
    --- linux-2.6.35.y.orig/net/llc/af_llc.c
    +++ linux-2.6.35.y/net/llc/af_llc.c
    @@ -317,8 +317,9 @@ static int llc_ui_bind(struct socket *so
    goto out;
    rc = -ENODEV;
    rtnl_lock();
    + rcu_read_lock();
    if (sk->sk_bound_dev_if) {
    - llc->dev = dev_get_by_index(&init_net, sk->sk_bound_dev_if);
    + llc->dev = dev_get_by_index_rcu(&init_net, sk->sk_bound_dev_if);
    if (llc->dev) {
    if (!addr->sllc_arphrd)
    addr->sllc_arphrd = llc->dev->type;
    @@ -329,13 +330,13 @@ static int llc_ui_bind(struct socket *so
    !llc_mac_match(addr->sllc_mac,
    llc->dev->dev_addr)) {
    rc = -EINVAL;
    - dev_put(llc->dev);
    llc->dev = NULL;
    }
    }
    } else
    llc->dev = dev_getbyhwaddr(&init_net, addr->sllc_arphrd,
    addr->sllc_mac);
    + rcu_read_unlock();
    rtnl_unlock();
    if (!llc->dev)
    goto out;
    --
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