From 5b28dde51d0ccc54cee70756e1800d70bed7114a Mon Sep 17 00:00:00 2001 From: Shuah Khan Date: Wed, 4 May 2016 16:48:28 -0300 Subject: [PATCH] [media] media: fix use-after-free in cdev_put() when app exits after driver unbind When driver unbinds while media_ioctl is in progress, cdev_put() fails with when app exits after driver unbinds. Add devnode struct device kobj as the cdev parent kobject. cdev_add() gets a reference to it and releases it in cdev_del() ensuring that the devnode is not deallocated as long as the application has the device file open. media_devnode_register() initializes the struct device kobj before calling cdev_add(). media_devnode_unregister() does cdev_del() and then deletes the device. devnode is released when the last reference to the struct device is gone. This problem is found on uvcvideo, em28xx, and au0828 drivers and fix has been tested on all three. kernel: [ 193.599736] BUG: KASAN: use-after-free in cdev_put+0x4e/0x50 kernel: [ 193.599745] Read of size 8 by task media_device_te/1851 kernel: [ 193.599792] INFO: Allocated in __media_device_register+0x54 kernel: [ 193.599951] INFO: Freed in media_devnode_release+0xa4/0xc0 kernel: [ 193.601083] Call Trace: kernel: [ 193.601093] [] dump_stack+0x67/0x94 kernel: [ 193.601102] [] print_trailer+0x112/0x1a0 kernel: [ 193.601111] [] object_err+0x34/0x40 kernel: [ 193.601119] [] kasan_report_error+0x224/0x530 kernel: [ 193.601128] [] ? kzfree+0x2d/0x40 kernel: [ 193.601137] [] ? kfree+0x1d2/0x1f0 kernel: [ 193.601154] [] ? cdev_put+0x4e/0x50 kernel: [ 193.601162] [] cdev_put+0x4e/0x50 kernel: [ 193.601170] [] __fput+0x52b/0x6c0 kernel: [ 193.601179] [] ? switch_task_namespaces+0x2a kernel: [ 193.601188] [] ____fput+0xe/0x10 kernel: [ 193.601196] [] task_work_run+0x133/0x1f0 kernel: [ 193.601204] [] ? switch_task_namespaces+0x5e kernel: [ 193.601213] [] do_exit+0x72c/0x2c20 kernel: [ 193.601224] [] ? release_task+0x1250/0x1250 - - - kernel: [ 193.601360] [] ? exit_to_usermode_loop+0xe7 kernel: [ 193.601368] [] exit_to_usermode_loop+0x120 kernel: [ 193.601376] [] syscall_return_slowpath+0x16a kernel: [ 193.601386] [] entry_SYSCALL_64_fastpath+0xa6 Signed-off-by: Shuah Khan Tested-by: Mauro Carvalho Chehab Signed-off-by: Mauro Carvalho Chehab --- drivers/media/media-device.c | 6 +++-- drivers/media/media-devnode.c | 48 +++++++++++++++++++++-------------- 2 files changed, 33 insertions(+), 21 deletions(-) diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c index e61fa66d95df..33a99524216a 100644 --- a/drivers/media/media-device.c +++ b/drivers/media/media-device.c @@ -723,16 +723,16 @@ int __must_check __media_device_register(struct media_device *mdev, ret = media_devnode_register(mdev, devnode, owner); if (ret < 0) { + /* devnode free is handled in media_devnode_*() */ mdev->devnode = NULL; - kfree(devnode); return ret; } ret = device_create_file(&devnode->dev, &dev_attr_model); if (ret < 0) { + /* devnode free is handled in media_devnode_*() */ mdev->devnode = NULL; media_devnode_unregister(devnode); - kfree(devnode); return ret; } @@ -812,6 +812,8 @@ void media_device_unregister(struct media_device *mdev) 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; } } EXPORT_SYMBOL_GPL(media_device_unregister); diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c index ecdc02d6ed83..5b605ff38daf 100644 --- a/drivers/media/media-devnode.c +++ b/drivers/media/media-devnode.c @@ -63,13 +63,8 @@ static void media_devnode_release(struct device *cd) struct media_devnode *devnode = to_media_devnode(cd); mutex_lock(&media_devnode_lock); - - /* Delete the cdev on this minor as well */ - cdev_del(&devnode->cdev); - /* Mark device node number as free */ clear_bit(devnode->minor, media_devnode_nums); - mutex_unlock(&media_devnode_lock); /* Release media_devnode and perform other cleanups as needed. */ @@ -77,6 +72,7 @@ static void media_devnode_release(struct device *cd) devnode->release(devnode); kfree(devnode); + pr_debug("%s: Media Devnode Deallocated\n", __func__); } static struct bus_type media_bus_type = { @@ -205,6 +201,8 @@ static int media_release(struct inode *inode, struct file *filp) /* decrease the refcount unconditionally since the release() return value is ignored. */ put_device(&devnode->dev); + + pr_debug("%s: Media Release\n", __func__); return 0; } @@ -235,6 +233,7 @@ int __must_check media_devnode_register(struct media_device *mdev, if (minor == MEDIA_NUM_DEVICES) { mutex_unlock(&media_devnode_lock); pr_err("could not get a free minor\n"); + kfree(devnode); return -ENFILE; } @@ -244,27 +243,31 @@ int __must_check media_devnode_register(struct media_device *mdev, devnode->minor = minor; devnode->media_dev = mdev; + /* Part 1: Initialize dev now to use dev.kobj for cdev.kobj.parent */ + devnode->dev.bus = &media_bus_type; + devnode->dev.devt = MKDEV(MAJOR(media_dev_t), devnode->minor); + devnode->dev.release = media_devnode_release; + if (devnode->parent) + devnode->dev.parent = devnode->parent; + dev_set_name(&devnode->dev, "media%d", devnode->minor); + device_initialize(&devnode->dev); + /* Part 2: Initialize and register the character device */ cdev_init(&devnode->cdev, &media_devnode_fops); devnode->cdev.owner = owner; + devnode->cdev.kobj.parent = &devnode->dev.kobj; ret = cdev_add(&devnode->cdev, MKDEV(MAJOR(media_dev_t), devnode->minor), 1); if (ret < 0) { pr_err("%s: cdev_add failed\n", __func__); - goto error; + goto cdev_add_error; } - /* Part 3: Register the media device */ - devnode->dev.bus = &media_bus_type; - devnode->dev.devt = MKDEV(MAJOR(media_dev_t), devnode->minor); - devnode->dev.release = media_devnode_release; - if (devnode->parent) - devnode->dev.parent = devnode->parent; - dev_set_name(&devnode->dev, "media%d", devnode->minor); - ret = device_register(&devnode->dev); + /* Part 3: Add the media device */ + ret = device_add(&devnode->dev); if (ret < 0) { - pr_err("%s: device_register failed\n", __func__); - goto error; + pr_err("%s: device_add failed\n", __func__); + goto device_add_error; } /* Part 4: Activate this minor. The char device can now be used. */ @@ -272,12 +275,15 @@ int __must_check media_devnode_register(struct media_device *mdev, return 0; -error: - mutex_lock(&media_devnode_lock); +device_add_error: cdev_del(&devnode->cdev); +cdev_add_error: + mutex_lock(&media_devnode_lock); clear_bit(devnode->minor, media_devnode_nums); + devnode->media_dev = NULL; mutex_unlock(&media_devnode_lock); + put_device(&devnode->dev); return ret; } @@ -289,8 +295,12 @@ void media_devnode_unregister(struct media_devnode *devnode) mutex_lock(&media_devnode_lock); clear_bit(MEDIA_FLAG_REGISTERED, &devnode->flags); + /* Delete the cdev on this minor as well */ + cdev_del(&devnode->cdev); mutex_unlock(&media_devnode_lock); - device_unregister(&devnode->dev); + device_del(&devnode->dev); + devnode->media_dev = NULL; + put_device(&devnode->dev); } /* -- 2.20.1