linux-kernel - [PATCH net v2] 9p/xen : Fix use after free bug in xen_9pfs_front

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Message-Id: <20230313165407.3766584-1-zyytlz.wz@163.com>
Date:   Tue, 14 Mar 2023 00:54:07 +0800
From:   Zheng Wang <zyytlz.wz@....com>
To:     ericvh@...il.com
Cc:     michal.swiatkowski@...ux.intel.com, lucho@...kov.net,
        asmadeus@...ewreck.org, linux_oss@...debyte.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, v9fs-developer@...ts.sourceforge.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        hackerzheng666@...il.com, 1395428693sheep@...il.com,
        alex000young@...il.com, Zheng Wang <zyytlz.wz@....com>
Subject: [PATCH net v2] 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 <zyytlz.wz@....com>
---
v2:
- fix type error of ring found by kernel test robot
---
 net/9p/trans_xen.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index c64050e839ac..83764431c066 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -274,12 +274,17 @@ static const struct xenbus_device_id xen_9pfs_front_ids[] = {
 static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
 {
 	int i, j;
+	struct xen_9pfs_dataring *ring = NULL;
 
 	write_lock(&xen_9pfs_lock);
 	list_del(&priv->list);
 	write_unlock(&xen_9pfs_lock);
 
 	for (i = 0; i < priv->num_rings; i++) {
+		/*cancel work*/
+		ring = &priv->rings[i];
+		cancel_work_sync(&ring->work);
+
 		if (!priv->rings[i].intf)
 			break;
 		if (priv->rings[i].irq > 0)
-- 
2.25.1