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From: Jason Gunthorpe <jgg@ziepe.ca>
To: "Håkon Bugge" <haakon.bugge@oracle.com>
Cc: Doug Ledford <dledford@redhat.com>, linux-rdma@vger.kernel.org
Subject: Re: [PATCH RDMA/uverbs] RDMA/uverbs: Protect list_empty() by lock
Date: Tue, 7 Jan 2020 14:42:38 -0400
Message-ID: <20200107184238.GA7928@ziepe.ca> (raw)
In-Reply-To: <20200106122711.217198-1-haakon.bugge@oracle.com>

On Mon, Jan 06, 2020 at 01:27:11PM +0100, Håkon Bugge wrote:
> In ib_uverbs_event_read(), events are waited for, then pulled off the
> kernel's event queue, and finally returned to user space.
> 
> There is an explicit check to see if the device is gone, and if so and
> the there are no events pending, an -EIO is returned.
> 
> However, said test does not check for queue empty whilst holding the
> lock, so there is a race where the existing code perceives the queue
> to be empty, when it in fact isn't. Fixed by acquiring the lock ahead
> of the list_empty() test.
> 
> Fixes: 036b10635739 ("IB/uverbs: Enable device removal when there are active user space applications")
> Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
> ---
>  drivers/infiniband/core/uverbs_main.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
> index 970d8e31dd65..7165e51790ed 100644
> --- a/drivers/infiniband/core/uverbs_main.c
> +++ b/drivers/infiniband/core/uverbs_main.c
> @@ -245,12 +245,14 @@ static ssize_t ib_uverbs_event_read(struct ib_uverbs_event_queue *ev_queue,
>  					     !uverbs_file->device->ib_dev)))
>  			return -ERESTARTSYS;
>  
> +		spin_lock_irq(&ev_queue->lock);
> +
>  		/* If device was disassociated and no event exists set an error */
>  		if (list_empty(&ev_queue->event_list) &&
> -		    !uverbs_file->device->ib_dev)
> +		    !uverbs_file->device->ib_dev) {
> +			spin_unlock_irq(&ev_queue->lock);
>  			return -EIO;

I noticed this too last month. While this patch is an improvement, I
had written this one which also fixes the wrong use of devce->ib_dev
without a READ_ONCE or locking. It is just winding its way through
testing right now.

What do you think?

From 37ddee0ea682eaf47e6167a090ae0a4e943f7f68 Mon Sep 17 00:00:00 2001
From: Jason Gunthorpe <jgg@mellanox.com>
Date: Tue, 26 Nov 2019 20:58:04 -0400
Subject: [PATCH] RDMA/core: Fix locking in ib_uverbs_event_read

This should not be using ib_dev to test for disassociation, during
disassociation is_closed is set under lock and the waitq is triggered.

Instead check is_closed and be sure to re-obtain the lock to test the
value after the wait_event returns.

Fixes: 036b10635739 ("IB/uverbs: Enable device removal when there are active user space applications")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 drivers/infiniband/core/uverbs_main.c | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 953a8c3fae64bd..2b7dc94b6a7a69 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -215,7 +215,6 @@ void ib_uverbs_release_file(struct kref *ref)
 }
 
 static ssize_t ib_uverbs_event_read(struct ib_uverbs_event_queue *ev_queue,
-				    struct ib_uverbs_file *uverbs_file,
 				    struct file *filp, char __user *buf,
 				    size_t count, loff_t *pos,
 				    size_t eventsz)
@@ -233,19 +232,16 @@ static ssize_t ib_uverbs_event_read(struct ib_uverbs_event_queue *ev_queue,
 
 		if (wait_event_interruptible(ev_queue->poll_wait,
 					     (!list_empty(&ev_queue->event_list) ||
-			/* The barriers built into wait_event_interruptible()
-			 * and wake_up() guarentee this will see the null set
-			 * without using RCU
-			 */
-					     !uverbs_file->device->ib_dev)))
+					      ev_queue->is_closed)))
 			return -ERESTARTSYS;
 
+		spin_lock_irq(&ev_queue->lock);
+
 		/* If device was disassociated and no event exists set an error */
-		if (list_empty(&ev_queue->event_list) &&
-		    !uverbs_file->device->ib_dev)
+		if (list_empty(&ev_queue->event_list) && ev_queue->is_closed) {
+			spin_unlock_irq(&ev_queue->lock);
 			return -EIO;
-
-		spin_lock_irq(&ev_queue->lock);
+		}
 	}
 
 	event = list_entry(ev_queue->event_list.next, struct ib_uverbs_event, list);
@@ -280,8 +276,7 @@ static ssize_t ib_uverbs_async_event_read(struct file *filp, char __user *buf,
 {
 	struct ib_uverbs_async_event_file *file = filp->private_data;
 
-	return ib_uverbs_event_read(&file->ev_queue, file->uverbs_file, filp,
-				    buf, count, pos,
+	return ib_uverbs_event_read(&file->ev_queue, filp, buf, count, pos,
 				    sizeof(struct ib_uverbs_async_event_desc));
 }
 
@@ -291,9 +286,8 @@ static ssize_t ib_uverbs_comp_event_read(struct file *filp, char __user *buf,
 	struct ib_uverbs_completion_event_file *comp_ev_file =
 		filp->private_data;
 
-	return ib_uverbs_event_read(&comp_ev_file->ev_queue,
-				    comp_ev_file->uobj.ufile, filp,
-				    buf, count, pos,
+	return ib_uverbs_event_read(&comp_ev_file->ev_queue, filp, buf, count,
+				    pos,
 				    sizeof(struct ib_uverbs_comp_event_desc));
 }
 
-- 
2.24.1


  reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-06 12:27 Håkon Bugge
2020-01-07 18:42 ` Jason Gunthorpe [this message]
2020-01-08 14:23   ` Håkon Bugge

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