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SubjectRe: [PATCH v2] Input: uinput: Avoid Object-Already-Free with a global lock
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Date

Hi Dmitry,

Can you please have a look at this patch ? as this seems to reproducing
quite frequently

Thanks,
Mukesh

On 4/10/2019 1:29 PM, Mukesh Ojha wrote:
> uinput_destroy_device() gets called from two places. In one place,
> uinput_ioctl_handler() where it is protected under a lock
> udev->mutex but there is no protection on udev device from freeing
> inside uinput_release().
>
> This can result in Object-Already-Free case where uinput parent
> device already got freed while a child being inserted inside it.
> That result in a double free case for parent while kernfs_put()
> being done for child in a failure path of adding a node.
>
> [ 160.093398] Call trace:
> [ 160.093417] kernfs_get+0x64/0x88
> [ 160.093438] kernfs_new_node+0x94/0xc8
> [ 160.093450] kernfs_create_dir_ns+0x44/0xfc
> [ 160.093463] sysfs_create_dir_ns+0xa8/0x130
> [ 160.093479] kobject_add_internal+0x278/0x650
> [ 160.093491] kobject_add_varg+0xe0/0x130
> [ 160.093502] kobject_add+0x15c/0x1d0
> [ 160.093518] device_add+0x2bc/0xde0
> [ 160.093533] input_register_device+0x5f4/0xa0c
> [ 160.093547] uinput_ioctl_handler+0x1184/0x2198
> [ 160.093560] uinput_ioctl+0x38/0x48
> [ 160.093573] vfs_ioctl+0x7c/0xb4
> [ 160.093585] do_vfs_ioctl+0x9ec/0x2350
> [ 160.093597] SyS_ioctl+0x6c/0xa4
> [ 160.093610] el0_svc_naked+0x34/0x38
> [ 160.093621] ---[ end trace bccf0093cda2c538 ]---
> [ 160.099041] =============================================================================
> [ 160.107459] BUG kernfs_node_cache (Tainted: G S W O ): Object already free
> [ 160.115235] -----------------------------------------------------------------------------
> [ 160.115235]
> [ 160.125151] Disabling lock debugging due to kernel taint
> [ 160.130626] INFO: Allocated in __kernfs_new_node+0x8c/0x3c0 age=11 cpu=2 pid=7098
> [ 160.138314] kmem_cache_alloc+0x358/0x388
> [ 160.142445] __kernfs_new_node+0x8c/0x3c0
> [ 160.146590] kernfs_new_node+0x80/0xc8
> [ 160.150462] kernfs_create_dir_ns+0x44/0xfc
> [ 160.154777] sysfs_create_dir_ns+0xa8/0x130
> [ 160.158416] CPU5: update max cpu_capacity 1024
> [ 160.159085] kobject_add_internal+0x278/0x650
> [ 160.163567] kobject_add_varg+0xe0/0x130
> [ 160.167606] kobject_add+0x15c/0x1d0
> [ 160.168452] CPU5: update max cpu_capacity 780
> [ 160.171287] get_device_parent+0x2d0/0x34c
> [ 160.175510] device_add+0x240/0xde0
> [ 160.178371] CPU6: update max cpu_capacity 916
> [ 160.179108] input_register_device+0x5f4/0xa0c
> [ 160.183686] uinput_ioctl_handler+0x1184/0x2198
> [ 160.188346] uinput_ioctl+0x38/0x48
> [ 160.191941] vfs_ioctl+0x7c/0xb4
> [ 160.195261] do_vfs_ioctl+0x9ec/0x2350
> [ 160.199111] SyS_ioctl+0x6c/0xa4
> [ 160.202436] INFO: Freed in kernfs_put+0x2c8/0x434 age=14 cpu=0 pid=7096
> [ 160.209230] kernfs_put+0x2c8/0x434
> [ 160.212825] kobject_del+0x50/0xcc
> [ 160.216332] cleanup_glue_dir+0x124/0x16c
> [ 160.220456] device_del+0x55c/0x5c8
> [ 160.224047] __input_unregister_device+0x274/0x2a8
> [ 160.228974] input_unregister_device+0x90/0xd0
> [ 160.233553] uinput_destroy_device+0x15c/0x1dc
> [ 160.238131] uinput_release+0x44/0x5c
> [ 160.241898] __fput+0x1f4/0x4e4
> [ 160.245127] ____fput+0x20/0x2c
> [ 160.248358] task_work_run+0x9c/0x174
> [ 160.252127] do_notify_resume+0x104/0x6bc
> [ 160.256253] work_pending+0x8/0x14
> [ 160.259751] INFO: Slab 0xffffffbf0215ff00 objects=33 used=11 fp=0xffffffc0857ffd08 flags=0x8101
> [ 160.268693] INFO: Object 0xffffffc0857ffd08 @offset=15624 fp=0xffffffc0857fefb0
> [ 160.268693]
> [ 160.277721] Redzone ffffffc0857ffd00: bb bb bb bb bb bb bb bb ........
> [ 160.286656] Object ffffffc0857ffd08: 00 00 00 00 01 00 00 80 58 a2 37 45 c1 ff ff ff ........X.7E....
> [ 160.296207] Object ffffffc0857ffd18: ae 21 10 0b 90 ff ff ff 20 fd 7f 85 c0 ff ff ff .!...... .......
> [ 160.305780] Object ffffffc0857ffd28: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> [ 160.315342] Object ffffffc0857ffd38: 00 00 00 00 00 00 00 00 7d a3 25 69 00 00 00 00 ........}.%i....
> [ 160.324896] Object ffffffc0857ffd48: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> [ 160.334446] Object ffffffc0857ffd58: 80 c0 28 47 c1 ff ff ff 00 00 00 00 00 00 00 00 ..(G............
> [ 160.344000] Object ffffffc0857ffd68: 80 4a ce d1 c0 ff ff ff dc 32 01 00 01 00 00 00 .J.......2......
> [ 160.353554] Object ffffffc0857ffd78: 11 00 ed 41 00 00 00 00 00 00 00 00 00 00 00 00 ...A............
> [ 160.363099] Redzone ffffffc0857ffd88: bb bb bb bb bb bb bb bb ........
> [ 160.372032] Padding ffffffc0857ffee0: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
> [ 160.378299] CPU6: update max cpu_capacity 780
> [ 160.380971] CPU: 4 PID: 7098 Comm: syz-executor Tainted: G S B W O 4.14.98+ #1
>
> So, avoid the race by taking a global lock inside uinput_release().
>
> Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
> Cc: Gaurav Kohli <gkohli@codeaurora.org>
> Cc: Peter Hutterer <peter.hutterer@who-t.net>
> Cc: Martin Kepplinger <martink@posteo.de>
> Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
> ---
> Also, if this looks good we can further use this global lock inside
> read/write in separate patches and release can happen at any time.
>
> Changes from v1->v2:
> - Mistakenly added udev lock replaced by global lock.
>
>
>
>
> drivers/input/misc/uinput.c | 28 ++++++++++++++++++++++++++--
> 1 file changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> index 26ec603f..2e7e096 100644
> --- a/drivers/input/misc/uinput.c
> +++ b/drivers/input/misc/uinput.c
> @@ -81,6 +81,8 @@ struct uinput_device {
> spinlock_t requests_lock;
> };
>
> +static DEFINE_MUTEX(uinput_glb_mutex);
> +
> static int uinput_dev_event(struct input_dev *dev,
> unsigned int type, unsigned int code, int value)
> {
> @@ -714,10 +716,18 @@ static __poll_t uinput_poll(struct file *file, poll_table *wait)
> static int uinput_release(struct inode *inode, struct file *file)
> {
> struct uinput_device *udev = file->private_data;
> + ssize_t retval;
> +
> + retval = mutex_lock_interruptible(&uinput_glb_mutex);
> + if (retval)
> + return retval;
>
> uinput_destroy_device(udev);
> + file->private_data = NULL;
> kfree(udev);
>
> + mutex_unlock(&uinput_glb_mutex);
> +
> return 0;
> }
>
> @@ -848,7 +858,7 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
> unsigned long arg, void __user *p)
> {
> int retval;
> - struct uinput_device *udev = file->private_data;
> + struct uinput_device *udev;
> struct uinput_ff_upload ff_up;
> struct uinput_ff_erase ff_erase;
> struct uinput_request *req;
> @@ -856,10 +866,20 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
> const char *name;
> unsigned int size;
>
> - retval = mutex_lock_interruptible(&udev->mutex);
> + retval = mutex_lock_interruptible(&uinput_glb_mutex);
> if (retval)
> return retval;
>
> + udev = file->private_data;
> + if (!udev) {
> + retval = -EINVAL;
> + goto unlock_glb_mutex;
> + }
> +
> + retval = mutex_lock_interruptible(&udev->mutex);
> + if (retval)
> + goto unlock_glb_mutex;
> +
> if (!udev->dev) {
> udev->dev = input_allocate_device();
> if (!udev->dev) {
> @@ -1039,8 +1059,12 @@ static long uinput_ioctl_handler(struct file *file, unsigned int cmd,
> }
>
> retval = -EINVAL;
> +
> out:
> mutex_unlock(&udev->mutex);
> +
> + unlock_glb_mutex:
> + mutex_unlock(&uinput_glb_mutex);
> return retval;
> }
>

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