[PATCH] media: dvbdev: fix dangling minor pointer in dvb_register_device() error paths

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

dvb_register_device() stores the dvb_device in the global dvb_minors[]
array via dvb_device_get() and releases minor_rwsem before calling
dvb_register_media_device() and device_create(). If either of these
fails, the error paths call kfree() on dvbdev without clearing the
dvb_minors[minor] entry and without going through dvb_device_put().
This leaves a stale pointer in the array that dvb_device_open() can
dereference under minor_rwsem, and bypasses the reference count
established by dvb_device_get().

Fix both error paths by:

1. Clearing dvb_minors[minor] under minor_rwsem and calling
   dvb_device_put() to release the array reference.
2. Replacing the direct kfree() with dvb_device_put() to release
   the initial reference and allow the release callback to free
   the object when the count reaches zero.

This mirrors the cleanup sequence in dvb_unregister_device().

Fixes: 0fc044b2b5e2 ("media: dvbdev: adopts refcnt to avoid UAF")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 drivers/media/dvb-core/dvbdev.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
index d753d329502a6..c931c467d4c52 100644
--- a/drivers/media/dvb-core/dvbdev.c
+++ b/drivers/media/dvb-core/dvbdev.c
@@ -551,6 +551,10 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 	if (ret) {
 		pr_err("%s: dvb_register_media_device failed to create the mediagraph\n",
 		       __func__);
+		down_write(&minor_rwsem);
+		dvb_minors[minor] = NULL;
+		dvb_device_put(dvbdev);
+		up_write(&minor_rwsem);
 		if (new_node) {
 			list_del(&new_node->list_head);
 			kfree(dvbdevfops);
@@ -558,7 +562,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		}
 		dvb_media_device_free(dvbdev);
 		list_del(&dvbdev->list_head);
-		kfree(dvbdev);
+		dvb_device_put(dvbdev);
 		*pdvbdev = NULL;
 		mutex_unlock(&dvbdev_register_lock);
 		return ret;
@@ -570,6 +574,10 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 	if (IS_ERR(clsdev)) {
 		pr_err("%s: failed to create device dvb%d.%s%d (%pe)\n",
 		       __func__, adap->num, dnames[type], id, clsdev);
+		down_write(&minor_rwsem);
+		dvb_minors[minor] = NULL;
+		dvb_device_put(dvbdev);
+		up_write(&minor_rwsem);
 		if (new_node) {
 			list_del(&new_node->list_head);
 			kfree(dvbdevfops);
@@ -577,7 +585,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		}
 		dvb_media_device_free(dvbdev);
 		list_del(&dvbdev->list_head);
-		kfree(dvbdev);
+		dvb_device_put(dvbdev);
 		*pdvbdev = NULL;
 		mutex_unlock(&dvbdev_register_lock);
 		return PTR_ERR(clsdev);
-- 
2.47.3