Re: [PATCH v2 0/3] vhost_task: Fix a bug where KVM wakes an exited task
From: Sean Christopherson <seanjc@google.com>
Date: 2025-08-28 00:16:37
Also in:
kvm, lkml, virtualization
On Wed, Aug 27, 2025, Sebastian Andrzej Siewior wrote:
On 2025-08-27 12:41:04 [-0700], Sean Christopherson wrote:quoted
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).
quoted hunk ↗ jump to hunk
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 <seanjc@google.com>