Patch "media: dvb-core: Fix use-after-free due on race condition at dvb_net" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    media: dvb-core: Fix use-after-free due on race condition at dvb_net

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     media-dvb-core-fix-use-after-free-due-on-race-condit.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a92aa7cc64acc27195f8ac8e067b89ce7d039a4c
Author: Hyunwoo Kim <imv4bel@xxxxxxxxx>
Date:   Thu Nov 17 04:59:23 2022 +0000

    media: dvb-core: Fix use-after-free due on race condition at dvb_net
    
    [ Upstream commit 4172385b0c9ac366dcab78eda48c26814b87ed1a ]
    
    A race condition may occur between the .disconnect function, which
    is called when the device is disconnected, and the dvb_device_open()
    function, which is called when the device node is open()ed.
    This results in several types of UAFs.
    
    The root cause of this is that you use the dvb_device_open() function,
    which does not implement a conditional statement
    that checks 'dvbnet->exit'.
    
    So, add 'remove_mutex` to protect 'dvbnet->exit' and use
    locked_dvb_net_open() function to check 'dvbnet->exit'.
    
    [mchehab: fix a checkpatch warning]
    
    Link: https://lore.kernel.org/linux-media/20221117045925.14297-3-imv4bel@xxxxxxxxx
    Signed-off-by: Hyunwoo Kim <imv4bel@xxxxxxxxx>
    Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/media/dvb-core/dvb_net.c b/drivers/media/dvb-core/dvb_net.c
index 9fed06ba88efb..ccaaabaaeb571 100644
--- a/drivers/media/dvb-core/dvb_net.c
+++ b/drivers/media/dvb-core/dvb_net.c
@@ -1564,15 +1564,43 @@ static long dvb_net_ioctl(struct file *file,
 	return dvb_usercopy(file, cmd, arg, dvb_net_do_ioctl);
 }
 
+static int locked_dvb_net_open(struct inode *inode, struct file *file)
+{
+	struct dvb_device *dvbdev = file->private_data;
+	struct dvb_net *dvbnet = dvbdev->priv;
+	int ret;
+
+	if (mutex_lock_interruptible(&dvbnet->remove_mutex))
+		return -ERESTARTSYS;
+
+	if (dvbnet->exit) {
+		mutex_unlock(&dvbnet->remove_mutex);
+		return -ENODEV;
+	}
+
+	ret = dvb_generic_open(inode, file);
+
+	mutex_unlock(&dvbnet->remove_mutex);
+
+	return ret;
+}
+
 static int dvb_net_close(struct inode *inode, struct file *file)
 {
 	struct dvb_device *dvbdev = file->private_data;
 	struct dvb_net *dvbnet = dvbdev->priv;
 
+	mutex_lock(&dvbnet->remove_mutex);
+
 	dvb_generic_release(inode, file);
 
-	if(dvbdev->users == 1 && dvbnet->exit == 1)
+	if (dvbdev->users == 1 && dvbnet->exit == 1) {
+		mutex_unlock(&dvbnet->remove_mutex);
 		wake_up(&dvbdev->wait_queue);
+	} else {
+		mutex_unlock(&dvbnet->remove_mutex);
+	}
+
 	return 0;
 }
 
@@ -1580,7 +1608,7 @@ static int dvb_net_close(struct inode *inode, struct file *file)
 static const struct file_operations dvb_net_fops = {
 	.owner = THIS_MODULE,
 	.unlocked_ioctl = dvb_net_ioctl,
-	.open =	dvb_generic_open,
+	.open =	locked_dvb_net_open,
 	.release = dvb_net_close,
 	.llseek = noop_llseek,
 };
@@ -1599,10 +1627,13 @@ void dvb_net_release (struct dvb_net *dvbnet)
 {
 	int i;
 
+	mutex_lock(&dvbnet->remove_mutex);
 	dvbnet->exit = 1;
+	mutex_unlock(&dvbnet->remove_mutex);
+
 	if (dvbnet->dvbdev->users < 1)
 		wait_event(dvbnet->dvbdev->wait_queue,
-				dvbnet->dvbdev->users==1);
+				dvbnet->dvbdev->users == 1);
 
 	dvb_unregister_device(dvbnet->dvbdev);
 
@@ -1621,6 +1652,7 @@ int dvb_net_init (struct dvb_adapter *adap, struct dvb_net *dvbnet,
 	int i;
 
 	mutex_init(&dvbnet->ioctl_mutex);
+	mutex_init(&dvbnet->remove_mutex);
 	dvbnet->demux = dmx;
 
 	for (i=0; i<DVB_NET_DEVICES_MAX; i++)
diff --git a/include/media/dvb_net.h b/include/media/dvb_net.h
index 5e31d37f25fac..cc01dffcc9f35 100644
--- a/include/media/dvb_net.h
+++ b/include/media/dvb_net.h
@@ -41,6 +41,9 @@
  * @exit:		flag to indicate when the device is being removed.
  * @demux:		pointer to &struct dmx_demux.
  * @ioctl_mutex:	protect access to this struct.
+ * @remove_mutex:	mutex that avoids a race condition between a callback
+ *			called when the hardware is disconnected and the
+ *			file_operations of dvb_net.
  *
  * Currently, the core supports up to %DVB_NET_DEVICES_MAX (10) network
  * devices.
@@ -53,6 +56,7 @@ struct dvb_net {
 	unsigned int exit:1;
 	struct dmx_demux *demux;
 	struct mutex ioctl_mutex;
+	struct mutex remove_mutex;
 };
 
 /**