linux-kernel - Re: [PATCH] drivers/media/rc: Fix a race condition in send

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Date:   Thu, 10 Nov 2022 22:12:24 +0530
From:   Gautam Menghani <gautammenghani201@...il.com>
To:     sean@...s.org, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+0c3cb6dc05fbbdc3ad66@...kaller.appspotmail.com
Subject: Re: [PATCH] drivers/media/rc: Fix a race condition in send_packet()

On Mon, Oct 31, 2022 at 10:20:15AM +0530, Gautam Menghani wrote:
> On Wed, Oct 19, 2022 at 10:32:14AM +0530, Gautam Menghani wrote:
> > The function send_packet() has a race condition as follows:
> > func send_packet()
> > {
> >     // do work
> >     call usb_submit_urb()
> >     mutex_unlock()
> >     wait_for_event_interruptible()  <-- lock gone
> >     mutex_lock()
> > }
> > 
> > func vfd_write()
> > {
> >     mutex_lock()
> >     call send_packet()  <- prev call is not completed
> >     mutex_unlock()
> > }
> > 
> > When the mutex is unlocked and the function send_packet() waits for the
> > call to complete, vfd_write() can start another call, which leads to the
> > "URB submitted while active" warning in usb_submit_urb(). 
> > Fix this by removing the mutex_unlock() call in send_packet() and using
> > mutex_lock_interruptible().
> > 
> > Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
> > Link: https://syzkaller.appspot.com/bug?id=e378e6a51fbe6c5cc43e34f131cc9a315ef0337e
> > Reported-by: syzbot+0c3cb6dc05fbbdc3ad66@...kaller.appspotmail.com
> > 
> > Signed-off-by: Gautam Menghani <gautammenghani201@...il.com>
> > ---
> >  drivers/media/rc/imon.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
> > index 735b925da998..91d8056666ec 100644
> > --- a/drivers/media/rc/imon.c
> > +++ b/drivers/media/rc/imon.c
> > @@ -646,15 +646,14 @@ static int send_packet(struct imon_context *ictx)
> >  		pr_err_ratelimited("error submitting urb(%d)\n", retval);
> >  	} else {
> >  		/* Wait for transmission to complete (or abort) */
> > -		mutex_unlock(&ictx->lock);
> >  		retval = wait_for_completion_interruptible(
> >  				&ictx->tx.finished);
> >  		if (retval) {
> >  			usb_kill_urb(ictx->tx_urb);
> >  			pr_err_ratelimited("task interrupted\n");
> >  		}
> > -		mutex_lock(&ictx->lock);
> >  
> > +		ictx->tx.busy = false;
> >  		retval = ictx->tx.status;
> >  		if (retval)
> >  			pr_err_ratelimited("packet tx failed (%d)\n", retval);
> > @@ -955,7 +954,8 @@ static ssize_t vfd_write(struct file *file, const char __user *buf,
> >  	if (ictx->disconnected)
> >  		return -ENODEV;
> >  
> > -	mutex_lock(&ictx->lock);
> > +	if (mutex_lock_interruptible(&ictx->lock))
> > +		return -ERESTARTSYS;
> >  
> >  	if (!ictx->dev_present_intf0) {
> >  		pr_err_ratelimited("no iMON device present\n");
> > -- 
> > 2.34.1
> > 
> 
> Hi,
> 
> Please review the above fix and let me know if any changes are required.
> 
> Thanks,
> Gautam

Hi,

Please review this patch and let me know if this patch needs any changes.

Thanks,
Gautam