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authorShuah Khan <shuahkh@osg.samsung.com>2016-06-10 14:37:23 -0300
committerMauro Carvalho Chehab <mchehab@s-opensource.com>2016-06-15 17:59:28 -0300
commit6f0dd24a084a17f9984dd49dffbf7055bf123993 (patch)
treee50dbdce2f36d2136d956860f21ece4ff25d20ba /drivers/media/media-device.c
parent5b28dde51d0ccc54cee70756e1800d70bed7114a (diff)
[media] media: fix media devnode ioctl/syscall and unregister race
Media devnode open/ioctl could be in progress when media device unregister is initiated. System calls and ioctls check media device registered status at the beginning, however, there is a window where unregister could be in progress without changing the media devnode status to unregistered. process 1 process 2 fd = open(/dev/media0) media_devnode_is_registered() (returns true here) media_device_unregister() (unregister is in progress and devnode isn't unregistered yet) ... ioctl(fd, ...) __media_ioctl() media_devnode_is_registered() (returns true here) ... media_devnode_unregister() ... (driver releases the media device memory) media_device_ioctl() (By this point devnode->media_dev does not point to allocated memory. use-after free in in mutex_lock_nested) BUG: KASAN: use-after-free in mutex_lock_nested+0x79c/0x800 at addr ffff8801ebe914f0 Fix it by clearing register bit when unregister starts to avoid the race. process 1 process 2 fd = open(/dev/media0) media_devnode_is_registered() (could return true here) media_device_unregister() (clear the register bit, then start unregister.) ... ioctl(fd, ...) __media_ioctl() media_devnode_is_registered() (return false here, ioctl returns I/O error, and will not access media device memory) ... media_devnode_unregister() ... (driver releases the media device memory) Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com> Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com> Reported-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com> Tested-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Diffstat (limited to 'drivers/media/media-device.c')
-rw-r--r--drivers/media/media-device.c15
1 files changed, 8 insertions, 7 deletions
diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index 33a99524216a..1795abeda658 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -732,6 +732,7 @@ int __must_check __media_device_register(struct media_device *mdev,
if (ret < 0) {
/* devnode free is handled in media_devnode_*() */
mdev->devnode = NULL;
+ media_devnode_unregister_prepare(devnode);
media_devnode_unregister(devnode);
return ret;
}
@@ -788,6 +789,9 @@ void media_device_unregister(struct media_device *mdev)
return;
}
+ /* Clear the devnode register bit to avoid races with media dev open */
+ media_devnode_unregister_prepare(mdev->devnode);
+
/* Remove all entities from the media device */
list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
__media_device_unregister_entity(entity);
@@ -808,13 +812,10 @@ void media_device_unregister(struct media_device *mdev)
dev_dbg(mdev->dev, "Media device unregistered\n");
- /* Check if mdev devnode was registered */
- if (media_devnode_is_registered(mdev->devnode)) {
- device_remove_file(&mdev->devnode->dev, &dev_attr_model);
- media_devnode_unregister(mdev->devnode);
- /* devnode free is handled in media_devnode_*() */
- mdev->devnode = NULL;
- }
+ device_remove_file(&mdev->devnode->dev, &dev_attr_model);
+ media_devnode_unregister(mdev->devnode);
+ /* devnode free is handled in media_devnode_*() */
+ mdev->devnode = NULL;
}
EXPORT_SYMBOL_GPL(media_device_unregister);

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