[PATCH v3 1/2] rpmsg: glink: Fix use-after-free in qcom_glink_rpdev_release()

[Sujit Kautkar]

qcom_glink_rpdev_release() sets channel->rpdev to NULL. However, with
debug enabled kernel, qcom_glink_rpdev_release() gets delayed due to
delayed kobject release and channel gets released by that time and
triggers below kernel warning. To avoid this use-after-free, clear ept
pointers during ept destroy and channel release and add a new condition
in qcom_glink_rpdev_release() to access channel

| BUG: KASAN: use-after-free in qcom_glink_rpdev_release+0x54/0x70
| Write of size 8 at addr ffffffaba438e8d0 by task kworker/6:1/54
|
| CPU: 6 PID: 54 Comm: kworker/6:1 Not tainted 5.4.109-lockdep #16
| Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
| Workqueue: events kobject_delayed_cleanup
| Call trace:
|  dump_backtrace+0x0/0x284
|  show_stack+0x20/0x2c
|  dump_stack+0xd4/0x170
|  print_address_description+0x3c/0x4a8
|  __kasan_report+0x144/0x168
|  kasan_report+0x10/0x18
|  __asan_report_store8_noabort+0x1c/0x24
|  qcom_glink_rpdev_release+0x54/0x70
|  device_release+0x68/0x14c
|  kobject_delayed_cleanup+0x158/0x2cc
|  process_one_work+0x7cc/0x10a4
|  worker_thread+0x80c/0xcec
|  kthread+0x2a8/0x314
|  ret_from_fork+0x10/0x18

Signed-off-by: Sujit Kautkar <sujitka@xxxxxxxxxxxx>
---
Changes in v3:
- Clear ept pointers and add extra conditions

Changes in v2:
- Fix typo in commit message

 drivers/rpmsg/qcom_glink_native.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
index e1444fefdd1c0..0c64a6f7a4f09 100644
--- a/drivers/rpmsg/qcom_glink_native.c
+++ b/drivers/rpmsg/qcom_glink_native.c
@@ -269,6 +269,9 @@ static void qcom_glink_channel_release(struct kref *ref)
 	idr_destroy(&channel->riids);
 	spin_unlock_irqrestore(&channel->intent_lock, flags);
 
+	if (channel->rpdev)
+		channel->rpdev->ept = NULL;
+
 	kfree(channel->name);
 	kfree(channel);
 }
@@ -1214,6 +1217,8 @@ static void qcom_glink_destroy_ept(struct rpmsg_endpoint *ept)
 	channel->ept.cb = NULL;
 	spin_unlock_irqrestore(&channel->recv_lock, flags);
 
+	channel->rpdev->ept = NULL;
+
 	/* Decouple the potential rpdev from the channel */
 	channel->rpdev = NULL;
 
@@ -1371,9 +1376,12 @@ static const struct rpmsg_endpoint_ops glink_endpoint_ops = {
 static void qcom_glink_rpdev_release(struct device *dev)
 {
 	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
-	struct glink_channel *channel = to_glink_channel(rpdev->ept);
+	struct glink_channel *channel = NULL;
 
-	channel->rpdev = NULL;
+	if (rpdev->ept) {
+		channel = to_glink_channel(rpdev->ept);
+		channel->rpdev = NULL;
+	}
 	kfree(rpdev);
 }
 
-- 
2.31.0