Re: [PATCH] r8a66597: Fix a possible concurrency use-after-free bug in r8a66597_endpoint_disable()

[Jia-Ju Bai]

On 2018/12/18 19:11, Greg KH wrote:
> On Tue, Dec 18, 2018 at 06:00:20PM +0800, Jia-Ju Bai wrote:
> > The function r8a66597_endpoint_disable() and r8a66597_urb_enqueue() may
> > be concurrently executed.
> > The two functions both access a possible shared variable "hep->hcpriv".
> >
> > This shared variable is freed by r8a66597_endpoint_disable() via the
> > call path:
> > r8a66597_endpoint_disable
> >    kfree(hep->hcpriv) (line 1995 in Linux-4.19)
> >
> > This variable is read by r8a66597_urb_enqueue() via the call path:
> > r8a66597_urb_enqueue
> >    spin_lock_irqsave(&r8a66597->lock);
> >    init_pipe_info
> >      enable_r8a66597_pipe
> >        pipe = hep->hcpriv (line 802 in Linux-4.19)
> >
> > The read operation is protected by a spinlock, but the free operation
> > is not protected by this spinlock, thus a concurrency use-after-free bug
> > may occur.
> >
> > To fix this bug, the spin-lock and spin-unlock function calls in
> > r8a66597_endpoint_disable() are moved to protect the free operation.
> >
> > Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
> > ---
> >   drivers/usb/host/r8a66597-hcd.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/host/r8a66597-hcd.c b/drivers/usb/host/r8a66597-hcd.c
> > index 984892dd72f5..1495ce14ad22 100644
> > --- a/drivers/usb/host/r8a66597-hcd.c
> > +++ b/drivers/usb/host/r8a66597-hcd.c
> > @@ -1991,13 +1991,14 @@ static void r8a66597_endpoint_disable(struct usb_hcd *hcd,
> >   		return;
> >   	pipenum = pipe->info.pipenum;
> >   
> > +	spin_lock_irqsave(&r8a66597->lock, flags);
> Don't you also need the __aquires/__releases markings on this function
> in order to properly annotate it, like the rest of the driver has?

Okay, thanks for this suggestion :)
I will send a v2 patch.


Best wishes,
Jia-Ju Bai