Re: [PATCH v2] misc: fastrpc: Fix a Use after-free-bug by race condition

[Greg Kroah-Hartman]

On Thu, Apr 27, 2023 at 06:29:16PM +0900, sangsup lee wrote:
> Is there any comment for this issue?

What issue?

> (reference: https://www.spinics.net/lists/kernel/msg4731408.html)

Please use lore.kernel.org links, we have no control over any other
random email archive .

And the above link just points to this proposed patch.

> 
> 
> 2023년 3월 23일 (목) 오전 10:37, Sangsup Lee <k1rh4.lee@xxxxxxxxx>님이 작성:
> >
> > From: Sangsup lee <k1rh4.lee@xxxxxxxxx>
> >
> > This patch adds mutex_lock for fixing an Use-after-free bug.
> > fastrpc_req_munmap_impl can be called concurrently in multi-threded environments.
> > The buf which is allocated by list_for_each_safe can be used after another thread frees it.

How was this tested?

> >
> > Signed-off-by: Sangsup lee <k1rh4.lee@xxxxxxxxx>
> > ---
> >  V1 -> V2: moving the locking to ioctl.
> >
> >  drivers/misc/fastrpc.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > index 93ebd174d848..aa1cf0e9f4ed 100644
> > --- a/drivers/misc/fastrpc.c
> > +++ b/drivers/misc/fastrpc.c
> > @@ -1901,7 +1901,9 @@ static long fastrpc_device_ioctl(struct file *file, unsigned int cmd,
> >                 err = fastrpc_req_mmap(fl, argp);
> >                 break;
> >         case FASTRPC_IOCTL_MUNMAP:
> > +               mutex_lock(&fl->mutex);
> >                 err = fastrpc_req_munmap(fl, argp);
> > +               mutex_unlock(&fl->mutex);

Are you sure you can call this function with the lock?  If so, why isn't
the mmap ioctl also locked?

thanks,

greg k-h