[SRU][Bionic, Focal, Jammy, Kinetic, OEM-5.14, OEM-5.17, OEM-6.0, OEM-6.1][PATCH 1/1] 9p/xen : Fix use after free bug in xen_9pfs_front_remove due to race condition

[John Cabaj]

From: Zheng Wang <zyytlz.wz at 163.com>

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 <zyytlz.wz at 163.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski at linux.intel.com>
Signed-off-by: Eric Van Hensbergen <ericvh at kernel.org>
(cherry picked from commit ea4f1009408efb4989a0f139b70fb338e7f687d0)
CVE-2023-1859
Signed-off-by: John Cabaj <john.cabaj at canonical.com>
---
 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 4255f2a3bea4..5d518a36fff7 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -300,6 +300,10 @@ 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)
-- 
2.34.1