netdev - Re: [PATCH v2 0/3] vhost_task: Fix a bug where KVM wakes an exited task

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Message-ID: <20250918133938-mutt-send-email-mst@kernel.org>
Date: Thu, 18 Sep 2025 13:40:25 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
	virtualization@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] vhost_task: Fix a bug where KVM wakes an exited
 task

On Thu, Sep 18, 2025 at 09:52:19AM -0700, Sean Christopherson wrote:
> On Thu, Sep 18, 2025, Michael S. Tsirkin wrote:
> > On Thu, Sep 18, 2025 at 09:04:07AM -0700, Sean Christopherson wrote:
> > > On Thu, Sep 18, 2025, Sebastian Andrzej Siewior wrote:
> > > > On 2025-09-18 11:09:05 [-0400], Michael S. Tsirkin wrote:
> > > > > So how about switching to this approach then?
> > > > > Instead of piling up fixes like we seem to do now ...
> > > 
> > > I don't have a strong preference for 6.17, beyond landing a fix of some kind.
> > > I think there are three options for 6.17, in order of "least like to break
> > > something":
> > > 
> > >  1. Sebastian's get_task_struct() fix
> > 
> > 
> > I am just a bit apprehensive that we don't create a situation
> > where we leak the task struct somehow, given the limited
> > testing time. Can you help me get convinced that risk is 0?
> 
> I doubt it, I share same similar concerns about lack of testing.  So I guess
> thinking about this again, #2 is probably safer since it'd only impact KVM?

I can't say I understand completely how we get that state though?
Why did the warning trigger if it's not a UAF?

> > >  2. This series, without the KILLED sanity check in __vhost_task_wake()
> > >  3. This series, with my fixup (with which syzbot was happy)