linux-kernel - Re: [PATCH v2] pps: fix warning in pps_register

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Message-ID: <aLkQs8gNkK9NfiOh@mozart.vkv.me>
Date: Wed, 3 Sep 2025 21:08:19 -0700
From: Calvin Owens <calvin@...nvd.org>
To: Wang Liang <wangliang74@...wei.com>
Cc: giometti@...eenne.com, gregkh@...uxfoundation.org, mschmidt@...hat.com,
	yuehaibing@...wei.com, zhangchangzhong@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] pps: fix warning in pps_register_cdev when register
 device fail

On Saturday 08/30 at 15:50 +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 Now the comment is outdated,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.
> 
> Thanks for the reminder from Calvin Owens, 'kfree_pps' should be removed
> in pps_register_source() to avoid a double free in the failure case.

Looks good to me, thanks for cleaning this up :)

Reviewed-By: Calvin Owens <calvin@...nvd.org>

> Link: https://lore.kernel.org/all/20250827065010.3208525-1-wangliang74@huawei.com/
> Fixes: c79a39dc8d06 ("pps: Fix a use-after-free")
> Signed-off-by: Wang Liang <wangliang74@...wei.com>
> ---
> v2: remove kfree_pps in pps_register_source().
> ---
>  drivers/pps/kapi.c | 5 +----
>  drivers/pps/pps.c  | 5 ++---
>  2 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
> index 92d1b62ea239..e9389876229e 100644
> --- a/drivers/pps/kapi.c
> +++ b/drivers/pps/kapi.c
> @@ -109,16 +109,13 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
>  	if (err < 0) {
>  		pr_err("%s: unable to create char device\n",
>  					info->name);
> -		goto kfree_pps;
> +		goto pps_register_source_exit;
>  	}
>  
>  	dev_dbg(&pps->dev, "new PPS source %s\n", info->name);
>  
>  	return pps;
>  
> -kfree_pps:
> -	kfree(pps);
> -
>  pps_register_source_exit:
>  	pr_err("%s: unable to register source\n", info->name);
>  
> diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
> index 9463232af8d2..c6b8b6478276 100644
> --- a/drivers/pps/pps.c
> +++ b/drivers/pps/pps.c
> @@ -374,6 +374,7 @@ int pps_register_cdev(struct pps_device *pps)
>  			       pps->info.name);
>  			err = -EBUSY;
>  		}
> +		kfree(pps);
>  		goto out_unlock;
>  	}
>  	pps->id = err;
> @@ -383,13 +384,11 @@ 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
>