[PATCH 6/6] media: dvb-core: wake up CA users on release

[Josef Schlehofer <pepe.schlehofer@gmail.com>]

dvb_ca_en50221_release() sets ca->exit and waits for open users to close
the CA device, but read, write, poll and ioctl can continue and blocked
readers and pollers are not woken.

Return -ENODEV from CA read, write and ioctl operations and EPOLLERR
from poll after ca->exit is set, and wake the corresponding wait queues.
Keep the release wait so the existing lifetime protection remains in
place.

tvheadend keeps the CA device open and waits for it with epoll, so it
needs to observe the disconnect before it can close the device.

Fixes: 280a8ab81733 ("media: dvb-core: Fix use-after-free due to race condition at dvb_ca_en50221")
Cc: stable@vger.kernel.org
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
---
 drivers/media/dvb-core/dvb_ca_en50221.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-core/dvb_ca_en50221.c b/drivers/media/dvb-core/dvb_ca_en50221.c
index 1b91ebb8f667..d478f995d5a9 100644
--- a/drivers/media/dvb-core/dvb_ca_en50221.c
+++ b/drivers/media/dvb-core/dvb_ca_en50221.c
@@ -1353,6 +1353,9 @@ static int dvb_ca_en50221_io_do_ioctl(struct file *file,
 
 	dprintk("%s\n", __func__);
 
+	if (ca->exit)
+		return -ENODEV;
+
 	if (mutex_lock_interruptible(&ca->ioctl_mutex))
 		return -ERESTARTSYS;
 
@@ -1460,6 +1463,9 @@ static ssize_t dvb_ca_en50221_io_write(struct file *file,
 
 	dprintk("%s\n", __func__);
 
+	if (ca->exit)
+		return -ENODEV;
+
 	/*
 	 * Incoming packet has a 2 byte header.
 	 * hdr[0] = slot_id, hdr[1] = connection_id
@@ -1618,6 +1624,9 @@ static ssize_t dvb_ca_en50221_io_read(struct file *file, char __user *buf,
 
 	dprintk("%s\n", __func__);
 
+	if (ca->exit)
+		return -ENODEV;
+
 	/*
 	 * Outgoing packet has a 2 byte header.
 	 * hdr[0] = slot_id, hdr[1] = connection_id
@@ -1635,8 +1644,11 @@ static ssize_t dvb_ca_en50221_io_read(struct file *file, char __user *buf,
 		/* wait for some data */
 		status = wait_event_interruptible(ca->wait_queue,
 						  dvb_ca_en50221_io_read_condition
-						  (ca, &result, &slot));
+						  (ca, &result, &slot) ||
+						  ca->exit);
 	}
+	if (ca->exit)
+		return -ENODEV;
 	if ((status < 0) || (result < 0)) {
 		if (result)
 			return result;
@@ -1819,6 +1831,9 @@ static __poll_t dvb_ca_en50221_io_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &ca->wait_queue, wait);
 
+	if (ca->exit)
+		return EPOLLERR;
+
 	if (dvb_ca_en50221_io_read_condition(ca, &result, &slot) == 1)
 		mask |= EPOLLIN;
 
@@ -1965,6 +1980,13 @@ void dvb_ca_en50221_release(struct dvb_ca_en50221 *pubca)
 	ca->exit = 1;
 	mutex_unlock(&ca->remove_mutex);
 
+	/*
+	 * Wake up everyone blocked in read() or poll() on the CA device, so
+	 * that they see the error and close it. The wait below cannot finish
+	 * before the last user has closed the device.
+	 */
+	wake_up_interruptible_all(&ca->wait_queue);
+
 	if (ca->dvbdev->users < 1)
 		wait_event(ca->dvbdev->wait_queue,
 				ca->dvbdev->users == 1);
-- 
2.54.0 (Apple Git-157)