Re: [PATCH v2] Input: uinput: Avoid Object-Already-Free with a global lock

[Al Viro]

On Tue, Apr 23, 2019 at 08:49:44AM +0000, dmitry.torokhov@xxxxxxxxx wrote:
> On Tue, Apr 23, 2019 at 12:51:13PM +0530, Mukesh Ojha wrote:

> > I have taken care this case from ioctl and release point of view.
> > 
> > Even if the release gets called first it will make the
> > file->private_data=NULL.
> > and further call to ioctl will not be a problem as the check is already
> > there.
> 
> Al, do we have any protections in VFS layer from userspace hanging onto
> a file descriptor and calling ioctl() on it even as another thread
> calls close() on the same fd?
> 
> Should the issue be solved by individual drivers, or more careful
> accounting for currently running operations is needed at VFS layer?

Neither.  An overlap of ->release() and ->ioctl() is possible only
if you've got memory corruption somewhere.

close() overlapping ioctl() is certainly possible, and won't trigger
that at all - sys_ioctl() holds onto reference to struct file, so
its refcount won't reach zero until we are done with it.