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Date: Fri, 23 Sep 2011 12:21:21 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
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To: "Serge E. Hallyn" <serge.hallyn@canonical.com>
cc: "Serge E. Hallyn" <serge@hallyn.com>, Greg KH <greg@kroah.com>,
        Oleg Nesterov <oleg@redhat.com>, lkml <linux-kernel@vger.kernel.org>,
        <richard@nod.at>, Andrew Morton <akpm@google.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>, Tejun Heo <tj@kernel.org>,
        <linux-usb@vger.kernel.org>
Subject: Re: [PATCH resend] user namespace: usb: make usb urbs user namespace
 aware (v2)
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On Fri, 23 Sep 2011, Serge E. Hallyn wrote:

> Quoting Alan Stern (stern@rowland.harvard.edu):
> > On Fri, 23 Sep 2011, Serge E. Hallyn wrote:
> > 
> > > (re-sending to Cc: Greg and linux-usb)
> > > 
> > > Add to the dev_state and alloc_async structures the user namespace
> > > corresponding to the uid and euid.  Pass these to kill_pid_info_as_uid(),
> > > which can then implement a proper, user-namespace-aware uid check.
> > > 
> > > Changelog:
> > > Sep 20: Per Oleg's suggestion: Instead of caching and passing user namespace,
> > > 	uid, and euid each separately, pass a struct cred.
> > 
> > This should be broken up into two separate patches: One to add
> > kill_pid_info_as_cred() and the other to modify the usbfs driver.
> 
> It seems like that would make the first patch harder to review (since
> it won't just show the changes from kill_pid_info_as_uid to
> kill_pid_info_as_cred), but I'll go ahead and split it up.  I assume
> kill_pid_info_as_uid should be removed in a third patch?

No, what I meant was that all the changes to /kernel/signal.c should be 
in one patch and all the changes to drivers/usb/core/devio.c should be 
in a second patch.

You did check to make sure there are no other references to
kill_pid_info_as_uid() in the kernel?

> > >  	if (signr)
> > > -		kill_pid_info_as_uid(sinfo.si_signo, &sinfo, pid, uid,
> > > -				      euid, secid);
> > > +		kill_pid_info_as_cred(sinfo.si_signo, &sinfo, pid, cred, secid);
> > 
> > This continues a bug that already exists in the current code.  Once 
> > ps->lock is released, there is no guarantee that the async structure 
> > will still exist.  It may already have been freed, and the reference to 
> 
> Yikes.  That makes sense.  I'll fix that for the cred and the pid as well
> then?

Right.

> > as->cred may already have been dropped.  That's why the local copies 
> > have to be made above.  cred shouldn't be a simple copy of as->cred; it 
> > should also increment the reference count.
> > 
> > > @@ -706,8 +705,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
> > >  	init_waitqueue_head(&ps->wait);
> > >  	ps->discsignr = 0;
> > >  	ps->disc_pid = get_pid(task_pid(current));
> > > -	ps->disc_uid = cred->uid;
> > > -	ps->disc_euid = cred->euid;
> > > +	ps->cred = get_cred(cred);
> > 
> > You might as well get rid of the "cred" local variable.  It isn't used 
> > for anything except this assignment.
> > 
> > Alan Stern
> 
> Thanks for looking, Alan.

You're welcome.

Alan Stern