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Tsirkin" To: Sean Christopherson Cc: Sebastian Andrzej Siewior , Paolo Bonzini , Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/3] vhost_task: Fix a bug where KVM wakes an exited task Message-ID: <20250915182232-mutt-send-email-mst@kernel.org> References: <20250827194107.4142164-1-seanjc@google.com> <20250827201059.EmmdDFB_@linutronix.de> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Aug 27, 2025 at 05:16:35PM -0700, Sean Christopherson wrote: > On Wed, Aug 27, 2025, Sebastian Andrzej Siewior wrote: > > On 2025-08-27 12:41:04 [-0700], Sean Christopherson wrote: > > > Michael, > > > > Sean, > > > > would the bellow work by chance? It is a quick shot but it looks > > symmetrical… > > Gah, sorry, I flagged your earlier mail and then forgot to circle back to it > (for whatever reason, I didn't entirely grok what you were suggesting). > > > diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c > > index bc738fa90c1d6..27107dcc1cbfe 100644 > > --- a/kernel/vhost_task.c > > +++ b/kernel/vhost_task.c > > @@ -100,6 +100,7 @@ void vhost_task_stop(struct vhost_task *vtsk) > > * freeing it below. > > */ > > wait_for_completion(&vtsk->exited); > > + put_task_struct(vtsk->task); > > kfree(vtsk); > > } > > EXPORT_SYMBOL_GPL(vhost_task_stop); > > @@ -148,7 +149,7 @@ struct vhost_task *vhost_task_create(bool (*fn)(void *), > > return ERR_CAST(tsk); > > } > > > > - vtsk->task = tsk; > > + vtsk->task = get_task_struct(tsk); > > return vtsk; > > } > > EXPORT_SYMBOL_GPL(vhost_task_create); > > Nice! This fixes things too. Either solution works for me. Or maybe do both? > Attempting to wake a task that vhost_task knows has exited (is exiting?) is a > bit gross, but even with that hardening, guarding against UAF is very nice to > have too. > > Tested-by: Sean Christopherson Sure let's do both. -- MST