linux-kernel - Re: [PATCH v2] can: mcba_usb: Fix memory leak when cancelling urb

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Date:   Mon, 11 Jan 2021 21:31:20 +0700
From:   Bui Quang Minh <minhquangbui99@...il.com>
To:     Oliver Neukum <oneukum@...e.de>
Cc:     linux-usb@...r.kernel.org, a.darwish@...utronix.de,
        bigeasy@...utronix.de, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, stern@...land.harvard.edu,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de
Subject: Re: [PATCH v2] can: mcba_usb: Fix memory leak when cancelling urb

On Mon, Jan 11, 2021 at 01:00:31PM +0100, Oliver Neukum wrote:
> Am Montag, den 11.01.2021, 10:49 +0000 schrieb Bui Quang Minh:
> > In mcba_usb_read_bulk_callback(), when we don't resubmit or fails to
> > resubmit the urb, we need to deallocate the transfer buffer that is
> > allocated in mcba_usb_start().
> > 
> > Reported-by: syzbot+57281c762a3922e14dfe@...kaller.appspotmail.com
> > Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> > ---
> > v1: add memory leak fix when not resubmitting urb
> > v2: add memory leak fix when failing to resubmit urb
> > 
> >  drivers/net/can/usb/mcba_usb.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/can/usb/mcba_usb.c b/drivers/net/can/usb/mcba_usb.c
> > index df54eb7d4b36..30236e640116 100644
> > --- a/drivers/net/can/usb/mcba_usb.c
> > +++ b/drivers/net/can/usb/mcba_usb.c
> > @@ -584,6 +584,8 @@ static void mcba_usb_read_bulk_callback(struct urb *urb)
> >  	case -EPIPE:
> >  	case -EPROTO:
> >  	case -ESHUTDOWN:
> > +		usb_free_coherent(urb->dev, urb->transfer_buffer_length,
> > +				  urb->transfer_buffer, urb->transfer_dma);
> >  		return;
> >  
> 
> Can you call usb_free_coherent() in what can be hard IRQ context?

You are right, I digged in the code and saw some comments that on some
architectures, usb_free_coherent() cannot be called in hard IRQ context.
I see the usb_free_coherent() is called in write_bulk_callback too. I will
send a patch that uses usb_anchor to keep track of these urbs and cleanup 
the transfer buffer later in disconnect().

Thank you for your review,
Quang Minh.