On Tue, 08 Mar 2022, Jason Wang wrote:
On Tue, Mar 8, 2022 at 3:18 AM Lee Jones lee.jones@linaro.org wrote:
vhost_vsock_handle_tx_kick() already holds the mutex during its call to vhost_get_vq_desc(). All we have to do here is take the same lock during virtqueue clean-up and we mitigate the reported issues.
Also WARN() as a precautionary measure. The purpose of this is to capture possible future race conditions which may pop up over time.
Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00
Cc: stable@vger.kernel.org Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com Signed-off-by: Lee Jones lee.jones@linaro.org
drivers/vhost/vhost.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 59edb5a1ffe28..ef7e371e3e649 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -693,6 +693,15 @@ void vhost_dev_cleanup(struct vhost_dev *dev) int i;
for (i = 0; i < dev->nvqs; ++i) {
/* No workers should run here by design. However, races have* previously occurred where drivers have been unable to flush* all work properly prior to clean-up. Without a successful* flush the guest will malfunction, but avoiding host memory* corruption in those cases does seem preferable.*/WARN_ON(mutex_is_locked(&dev->vqs[i]->mutex));I don't get how this can help, the mutex could be grabbed in the middle of the above and below line.
The worst that happens in this slim scenario is we miss a warning. The mutexes below will still function as expected and prevent possible memory corruption.
mutex_lock(&dev->vqs[i]->mutex); if (dev->vqs[i]->error_ctx) eventfd_ctx_put(dev->vqs[i]->error_ctx); if (dev->vqs[i]->kick)@@ -700,6 +709,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev) if (dev->vqs[i]->call_ctx.ctx) eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx); vhost_vq_reset(dev, dev->vqs[i]);
mutex_unlock(&dev->vqs[i]->mutex); }I'm not sure it's correct to assume some behaviour of a buggy device. For the device mutex, we use that to protect more than just err/call and vq.
When I authored this, I did so as *the* fix. However, since the cause of today's crash has now been patched, this has become a belt and braces solution. Michael's addition of the WARN() also has the benefit of providing us with an early warning system for future breakages. Personally, I think it's kinda neat.