2023-03-13 14:45:32

by Zheng Wang

Subject: [PATCH net v3] 9p/xen : Fix use after free bug in xen_9pfs_front_remove due to race condition

In xen_9pfs_front_probe, it calls xen_9pfs_front_alloc_dataring
to init priv->rings and bound &ring->work with p9_xen_response.

When it calls xen_9pfs_front_event_handler to handle IRQ requests,
it will finally call schedule_work to start the work.

When we call xen_9pfs_front_remove to remove the driver, there
may be a sequence as follows:

Fix it by finishing the work before cleanup in xen_9pfs_front_free.

Note that, this bug is found by static analysis, which might be
false positive.

CPU0 CPU1

|p9_xen_response
xen_9pfs_front_remove|
xen_9pfs_front_free|
kfree(priv) |
//free priv |
|p9_tag_lookup
|//use priv->client

Fixes: 71ebd71921e4 ("xen/9pfs: connect to the backend")
Signed-off-by: Zheng Wang <[email protected]>
---
v3:
- remove unnecessary comment and move definition to the
for loop suggested by Michal Swiatkowski

v2:
- fix type error of ring found by kernel test robot
---
net/9p/trans_xen.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index c64050e839ac..df467ffb52d0 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -280,6 +280,10 @@ static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
write_unlock(&xen_9pfs_lock);

for (i = 0; i < priv->num_rings; i++) {
+ struct xen_9pfs_dataring *ring = &priv->rings[i];
+
+ cancel_work_sync(&ring->work);
+
if (!priv->rings[i].intf)
break;
if (priv->rings[i].irq > 0)
--
2.25.1

2023-03-13 14:55:24

by Michal Swiatkowski

Subject: Re: [PATCH net v3] 9p/xen : Fix use after free bug in xen_9pfs_front_remove due to race condition

On Mon, Mar 13, 2023 at 10:43:25PM +0800, Zheng Wang wrote:
> In xen_9pfs_front_probe, it calls xen_9pfs_front_alloc_dataring
> to init priv->rings and bound &ring->work with p9_xen_response.
>
> When it calls xen_9pfs_front_event_handler to handle IRQ requests,
> it will finally call schedule_work to start the work.
>
> When we call xen_9pfs_front_remove to remove the driver, there
> may be a sequence as follows:
>
> Fix it by finishing the work before cleanup in xen_9pfs_front_free.
>
> Note that, this bug is found by static analysis, which might be
> false positive.
>
> CPU0 CPU1
>
> |p9_xen_response
> xen_9pfs_front_remove|
> xen_9pfs_front_free|
> kfree(priv) |
> //free priv |
> |p9_tag_lookup
> |//use priv->client
>
> Fixes: 71ebd71921e4 ("xen/9pfs: connect to the backend")
> Signed-off-by: Zheng Wang <[email protected]>
> ---
> v3:
> - remove unnecessary comment and move definition to the
> for loop suggested by Michal Swiatkowski
>
> v2:
> - fix type error of ring found by kernel test robot
> ---
> net/9p/trans_xen.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
[...]

Thanks for changes
Reviewed-by: Michal Swiatkowski <[email protected]>