Re: [PATCH net] ppp: ensure file->private_data can't be overridden

On Mon, Mar 14, 2016 at 02:57:59PM -0400, David Miller wrote:

From: Guillaume Nault <redacted>
Date: Mon, 14 Mar 2016 18:59:40 +0100

quoted

Testing ->private_data without lock in ppp_ioctl() before calling
ppp_unattached_ioctl() is fine, because either ->private_data is
not NULL and thus is stable, or it is and ppp_unattached_ioctl()
takes care of not overriding ->private_data, should its value get
modified before taking the mutex.

This is exactly the ambiguous behavior I want you to avoid.

The decision should be atomic from ppp_ioctl()'s test all the way
until ppp_unattached_ioctl() does it's work.

OK, will fix in v2.