With the current code, when vsock_dequeue_accept() is removing a sock
from the list, nothing prevents vsock_enqueue_accept() from adding a new
sock into the list concurrently. We should add a lock to protect the list.
Signed-off-by: Dexuan Cui <[email protected]>
Cc: Andy King <[email protected]>
Cc: Dmitry Torokhov <[email protected]>
Cc: George Zhang <[email protected]>
Cc: Jorgen Hansen <[email protected]>
Cc: Reilly Grant <[email protected]>
Cc: Asias He <[email protected]>
Cc: Stefan Hajnoczi <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Cathy Avery <[email protected]>
Cc: K. Y. Srinivasan <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Stephen Hemminger <[email protected]>
---
net/vmw_vsock/af_vsock.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index dfc8c51e..b7b2c66 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -126,6 +126,7 @@ static struct proto vsock_proto = {
static const struct vsock_transport *transport;
static DEFINE_MUTEX(vsock_register_mutex);
+static DEFINE_SPINLOCK(vsock_accept_queue_lock);
/**** EXPORTS ****/
@@ -406,7 +407,10 @@ void vsock_enqueue_accept(struct sock *listener, struct sock *connected)
sock_hold(connected);
sock_hold(listener);
+
+ spin_lock(&vsock_accept_queue_lock);
list_add_tail(&vconnected->accept_queue, &vlistener->accept_queue);
+ spin_unlock(&vsock_accept_queue_lock);
}
EXPORT_SYMBOL_GPL(vsock_enqueue_accept);
@@ -423,7 +427,10 @@ static struct sock *vsock_dequeue_accept(struct sock *listener)
vconnected = list_entry(vlistener->accept_queue.next,
struct vsock_sock, accept_queue);
+ spin_lock(&vsock_accept_queue_lock);
list_del_init(&vconnected->accept_queue);
+ spin_unlock(&vsock_accept_queue_lock);
+
sock_put(listener);
/* The caller will need a reference on the connected socket so we let
* it call sock_put().
--
2.7.4
> On Aug 16, 2017, at 12:15 AM, Dexuan Cui <[email protected]> wrote:
>
>
> With the current code, when vsock_dequeue_accept() is removing a sock
> from the list, nothing prevents vsock_enqueue_accept() from adding a new
> sock into the list concurrently. We should add a lock to protect the list.
>
For the VMCI socket transport, we always lock the sockets before calling into vsock_enqueue_accept and af_vsock.c locks the socket before calling vsock_dequeue_accept, so from our point of view these operations are already protected, but with finer granularity than a single global lock. As far as I can see, the virtio transport also locks the socket before calling vsock_enqueue_accept, so they should be fine with the current version as well, but Stefan can comment on that.
Thanks,
Jorgen
> > On Aug 16, 2017, at 12:15 AM, Dexuan Cui <[email protected]> wrote:
> > With the current code, when vsock_dequeue_accept() is removing a sock
> > from the list, nothing prevents vsock_enqueue_accept() from adding a new
> > sock into the list concurrently. We should add a lock to protect the list.
>
> For the VMCI socket transport, we always lock the sockets before calling into
> vsock_enqueue_accept and af_vsock.c locks the socket before calling
> vsock_dequeue_accept, so from our point of view these operations are already
> protected, but with finer granularity than a single global lock. As far as I can see,
> the virtio transport also locks the socket before calling vsock_enqueue_accept,
> so they should be fine with the current version as well, but Stefan can comment
> on that.
>
> Jorgen
Hi Jorgen,
Thanks, you're correct.
Please ignore this patch. I'll update the hv_sock driver to add proper
lock_sock()/relesae_sock().
Thanks,
-- Dexuan
On Tue, Aug 15, 2017 at 10:15:39PM +0000, Dexuan Cui wrote:
> With the current code, when vsock_dequeue_accept() is removing a sock
> from the list, nothing prevents vsock_enqueue_accept() from adding a new
> sock into the list concurrently. We should add a lock to protect the list.
The listener sock is locked, preventing concurrent modification. I have
checked both the virtio and vmci transports. Can you post an example
where the listener sock isn't locked?
Stefan
> From: Stefan Hajnoczi [mailto:[email protected]]
> Sent: Thursday, August 17, 2017 07:06
>
> On Tue, Aug 15, 2017 at 10:15:39PM +0000, Dexuan Cui wrote:
> > With the current code, when vsock_dequeue_accept() is removing a sock
> > from the list, nothing prevents vsock_enqueue_accept() from adding a new
> > sock into the list concurrently. We should add a lock to protect the list.
>
> The listener sock is locked, preventing concurrent modification. I have
> checked both the virtio and vmci transports. Can you post an example
> where the listener sock isn't locked?
>
> Stefan
Sorry, I was not careful when checking the vmci code.
Please ignore the patch.
Now I realized the expectation is that the individual transport drivers should
do the locking for vsock_enqueue_accept(), but for vsock_dequeue_accept(),
the locking is done by the common vsock driver.
Thanks,
-- Dexuan