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

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Message-ID: <aLBcgTpVO3VlVtM7@mozart.vkv.me>
Date: Thu, 28 Aug 2025 06:41:21 -0700
From: Calvin Owens <calvin@...nvd.org>
To: Wang Liang <wangliang74@...wei.com>
Cc: giometti@...eenne.com, mschmidt@...hat.com, gregkh@...uxfoundation.org,
	yuehaibing@...wei.com, zhangchangzhong@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pps: fix warning in pps_register_cdev when register
 device fail

On Thursday 08/28 at 17:24 +0800, Wang Liang wrote:
> 
> 在 2025/8/27 23:32, Calvin Owens 写道:
> > 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?
> 
> 
> I find this issue from my local syzkaller project.
> 
> Function pps_register_cdev() call the universal interface 'device_register',
> which can return error when kzalloc fail, or sysfs error, etc.
> 
> Hope the above information is helpful.

Thanks Wang, no worries, I just noticed it was under TIOCSETD and
thought syzcaller might've lucked into something interesting there too.

> ------
> Best regards
> Wang Liang
> 
> > 
> > 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@...nvd.org>
> > 
> > Thanks,
> > Calvin
> > 
> > > Fixes: c79a39dc8d06 ("pps: Fix a use-after-free")
> > > Signed-off-by: Wang Liang <wangliang74@...wei.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
> > >