[PATCH AUTOSEL 5.15 20/43] media: dvb-core: Fix use-after-free due on race condition at dvb_net

Sasha Levin
2023-05-25T18:47:23Z

From: Hyunwoo Kim <imv4bel@gmail.com>

[ 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@gmail.com
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/media/dvb-core/dvb_net.c | 38 +++++++++++++++++++++++++++++---
include/media/dvb_net.h | 4 ++++
2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_net.c b/drivers/media/dvb-core/dvb_net.c
index dddebea644bb8..c594b1bdfcaa5 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;
};

/**
--
2.39.2