linux-kernel - Re: [PATCH] vhost: Take a reference on the task that is reference in struct vhost

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250921165538-mutt-send-email-mst@kernel.org>
Date: Sun, 21 Sep 2025 16:56:16 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Sean Christopherson <seanjc@...gle.com>,
	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] vhost: Take a reference on the task that is reference in
 struct vhost_task.

Subject: that is reference -> that is referenced

On Thu, Sep 18, 2025 at 08:11:44PM +0200, Sebastian Andrzej Siewior wrote:
> vhost_task_create() creates a task and keeps a reference to its
> task_struct. That task may exit early via a signal and its task_struct
> will be released.
> A pending vhost_task_wake() will then attempt to wake the task and
> access a task_struct which is no longer there.
> 
> Acquire a reference on the task_struct while creating the thread and
> release the reference while the struct vhost_task itself is removed.
> If the task exits early due to a signal, then the vhost_task_wake() will
> still access a valid task_struct. The wake is safe and will be skipped
> in this case.
> 
> Fixes: f9010dbdce911 ("fork, vhost: Use CLONE_THREAD to fix freezer/ps regression")
> Reported-by: Sean Christopherson <seanjc@...gle.com>
> Closes: https://lore.kernel.org/all/aKkLEtoDXKxAAWju@google.com/
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  kernel/vhost_task.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> 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);
> -- 
> 2.51.0