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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxx>
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@xxxxxxxxxxxx>
---
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
