[PATCH V2 1/2] rpmsg: glink: Add lock to avoid race when rpmsg device is released

[Deepak Kumar Singh]

When remote host goes down glink char device channel is freed,
At the same time user space apps can still try to open/poll rpmsg
char device which will result in calling rpmsg_create_ept. This may
cause reference to already freed context of glink chardev channel and
result in below crash signatures -

1)
rpmsg_create_ept+0x40/0xa0
rpmsg_eptdev_open+0x88/0x138
chrdev_open+0xc4/0x1c8
do_dentry_open+0x230/0x378

2)
rpmsg_poll+0x5c/0x80
rpmsg_eptdev_poll+0x84/0xa4
do_sys_poll+0x22c/0x5c8

This patch adds proper lock and check condition to avoid such crash.

Signed-off-by: Deepak Kumar Singh <quic_deesin@xxxxxxxxxxx>
---
 drivers/rpmsg/rpmsg_char.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index 4f21891..5500dc0 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -75,6 +75,7 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
 	struct rpmsg_eptdev *eptdev = dev_to_eptdev(dev);
 
 	mutex_lock(&eptdev->ept_lock);
+	eptdev->rpdev = NULL;
 	if (eptdev->ept) {
 		rpmsg_destroy_ept(eptdev->ept);
 		eptdev->ept = NULL;
@@ -126,6 +127,11 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
 		return -EBUSY;
 	}
 
+	if (!eptdev->rpdev) {
+		mutex_unlock(&eptdev->ept_lock);
+		return -ENETRESET;
+	}
+
 	get_device(dev);
 
 	/*
@@ -277,7 +283,9 @@ static __poll_t rpmsg_eptdev_poll(struct file *filp, poll_table *wait)
 	if (!skb_queue_empty(&eptdev->queue))
 		mask |= EPOLLIN | EPOLLRDNORM;
 
+	mutex_lock(&eptdev->ept_lock);
 	mask |= rpmsg_poll(eptdev->ept, filp, wait);
+	mutex_unlock(&eptdev->ept_lock);
 
 	return mask;
 }
-- 
2.7.4