Re: [PATCH] pps: fix warning in pps_register_cdev when register device fail

[Calvin Owens <calvin@wbinvd.org>]

On Wednesday 08/27 at 14:50 +0800, Wang Liang wrote:
> Similar to previous commit 2a934fdb01db ("media: v4l2-dev: fix error
> handling in __video_register_device()"), the release hook should be set
> before device_register(). Otherwise, when device_register() return error
> and put_device() try to callback the release function, the below warning
> may happen.
> 
>   ------------[ cut here ]------------
>   WARNING: CPU: 1 PID: 4760 at drivers/base/core.c:2567 device_release+0x1bd/0x240 drivers/base/core.c:2567
>   Modules linked in:
>   CPU: 1 UID: 0 PID: 4760 Comm: syz.4.914 Not tainted 6.17.0-rc3+ #1 NONE
>   RIP: 0010:device_release+0x1bd/0x240 drivers/base/core.c:2567
>   Call Trace:
>    <TASK>
>    kobject_cleanup+0x136/0x410 lib/kobject.c:689
>    kobject_release lib/kobject.c:720 [inline]
>    kref_put include/linux/kref.h:65 [inline]
>    kobject_put+0xe9/0x130 lib/kobject.c:737
>    put_device+0x24/0x30 drivers/base/core.c:3797
>    pps_register_cdev+0x2da/0x370 drivers/pps/pps.c:402
>    pps_register_source+0x2f6/0x480 drivers/pps/kapi.c:108
>    pps_tty_open+0x190/0x310 drivers/pps/clients/pps-ldisc.c:57
>    tty_ldisc_open+0xa7/0x120 drivers/tty/tty_ldisc.c:432
>    tty_set_ldisc+0x333/0x780 drivers/tty/tty_ldisc.c:563
>    tiocsetd drivers/tty/tty_io.c:2429 [inline]
>    tty_ioctl+0x5d1/0x1700 drivers/tty/tty_io.c:2728
>    vfs_ioctl fs/ioctl.c:51 [inline]
>    __do_sys_ioctl fs/ioctl.c:598 [inline]
>    __se_sys_ioctl fs/ioctl.c:584 [inline]
>    __x64_sys_ioctl+0x194/0x210 fs/ioctl.c:584
>    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>    do_syscall_64+0x5f/0x2a0 arch/x86/entry/syscall_64.c:94
>    entry_SYSCALL_64_after_hwframe+0x76/0x7e
>    </TASK>
> 
> Before commit c79a39dc8d06 ("pps: Fix a use-after-free"),
> pps_register_cdev() call device_create() to create pps->dev, which will
> init dev->release to device_create_release(). Now the comment is outdated,
> just remove it.

Hi Wang,

I'm curious why pps_register_cdev() is failing, is there possibly a
second issue to investigate there? Or was it fault injection?

Otherwise, makes perfect sense to me. I'm new to this code, so grain of
salt, but since I exposed it:

Reviewed-by: Calvin Owens <calvin@wbinvd.org>

Thanks,
Calvin

> Fixes: c79a39dc8d06 ("pps: Fix a use-after-free")
> Signed-off-by: Wang Liang <wangliang74@huawei.com>
> ---
>  drivers/pps/pps.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
> index 9463232af8d2..0d2d57250575 100644
> --- a/drivers/pps/pps.c
> +++ b/drivers/pps/pps.c
> @@ -383,13 +383,11 @@ int pps_register_cdev(struct pps_device *pps)
>  	pps->dev.devt = MKDEV(pps_major, pps->id);
>  	dev_set_drvdata(&pps->dev, pps);
>  	dev_set_name(&pps->dev, "pps%d", pps->id);
> +	pps->dev.release = pps_device_destruct;
>  	err = device_register(&pps->dev);
>  	if (err)
>  		goto free_idr;
>  
> -	/* Override the release function with our own */
> -	pps->dev.release = pps_device_destruct;
> -
>  	pr_debug("source %s got cdev (%d:%d)\n", pps->info.name, pps_major,
>  		 pps->id);
>  
> -- 
> 2.33.0
>