media: dvbdev: prevent the risk of out of memory access

The dvbdev contains a static variable used to store dvb minors.

The behavior of it depends if CONFIG_DVB_DYNAMIC_MINORS is set
or not. When not set, dvb_register_device() won't check for
boundaries, as it will rely that a previous call to
dvb_register_adapter() would already be enforcing it.

On a similar way, dvb_device_open() uses the assumption
that the register functions already did the needed checks.

This can be fragile if some device ends using different
calls. This also generate warnings on static check analysers
like Coverity.

So, add explicit guards to prevent potential risk of OOM issues.

Fixes: 5dd3f30 ("V4L/DVB (9361): Dynamic DVB minor allocation")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Author: mchehab

drivers/media/dvb-core/dvbdev.c

@@ -86,10 +86,15 @@ static DECLARE_RWSEM(minor_rwsem);
 static int dvb_device_open(struct inode *inode, struct file *file)
 {
 	struct dvb_device *dvbdev;
+	unsigned int minor = iminor(inode);
+
+	if (minor >= MAX_DVB_MINORS)
+		return -ENODEV;
 
 	mutex_lock(&dvbdev_mutex);
 	down_read(&minor_rwsem);
-	dvbdev = dvb_minors[iminor(inode)];
+
+	dvbdev = dvb_minors[minor];
 
 	if (dvbdev && dvbdev->fops) {
 		int err = 0;
@@ -525,7 +530,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 	for (minor = 0; minor < MAX_DVB_MINORS; minor++)
 		if (!dvb_minors[minor])
 			break;
-	if (minor == MAX_DVB_MINORS) {
+	if (minor >= MAX_DVB_MINORS) {
 		if (new_node) {
 			list_del(&new_node->list_head);
 			kfree(dvbdevfops);
@@ -540,6 +545,14 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 	}
 #else
 	minor = nums2minor(adap->num, type, id);
+	if (minor >= MAX_DVB_MINORS) {
+		dvb_media_device_free(dvbdev);
+		list_del(&dvbdev->list_head);
+		kfree(dvbdev);
+		*pdvbdev = NULL;
+		mutex_unlock(&dvbdev_register_lock);
+		return ret;
+	}
 #endif
 	dvbdev->minor = minor;
 	dvb_minors[minor] = dvb_device_get(dvbdev);