Code: long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
{
	struct file *eventfp, *filep = NULL;
	struct eventfd_ctx *ctx = NULL;
	u64 p;
	long r;
	int i, fd;

	/* If you are not the owner, you can become one */
	if (ioctl == VHOST_SET_OWNER) {
		r = vhost_dev_set_owner(d);
		goto done;
	}

	/* You must be the owner to do anything else */
	r = vhost_dev_check_owner(d);
	if (r)
		goto done;

	switch (ioctl) {
	case VHOST_SET_MEM_TABLE:
		r = vhost_set_memory(d, argp);
		break;
	case VHOST_SET_LOG_BASE:
		if (copy_from_user(&p, argp, sizeof p)) {
			r = -EFAULT;
			break;
		}
		if ((u64)(unsigned long)p != p) {
			r = -EFAULT;
			break;
		}
		for (i = 0; i < d->nvqs; ++i) {
			struct vhost_virtqueue *vq;
			void __user *base = (void __user *)(unsigned long)p;
			vq = d->vqs[i];
			mutex_lock(&vq->mutex);
			/* If ring is inactive, will check when it's enabled. */
			if (vq->private_data && !vq_log_access_ok(vq, base))
				r = -EFAULT;
			else
				vq->log_base = base;
			mutex_unlock(&vq->mutex);
		}
		break;
	case VHOST_SET_LOG_FD:
		r = get_user(fd, (int __user *)argp);
		if (r < 0)
			break;
		eventfp = fd == -1 ? NULL : eventfd_fget(fd);
		if (IS_ERR(eventfp)) {
			r = PTR_ERR(eventfp);
			break;
 		}
 		if (eventfp != d->log_file) {
 			filep = d->log_file;
 			ctx = d->log_ctx;
 			d->log_ctx = eventfp ?
 				eventfd_ctx_fileget(eventfp) : NULL;
		} else
			filep = eventfp;
		for (i = 0; i < d->nvqs; ++i) {
			mutex_lock(&d->vqs[i]->mutex);
			d->vqs[i]->log_ctx = d->log_ctx;
			mutex_unlock(&d->vqs[i]->mutex);
		}
		if (ctx)
			eventfd_ctx_put(ctx);
		if (filep)
			fput(filep);
		break;
	default:
		r = -ENOIOCTLCMD;
		break;
	}
done:
	return r;
}

Vulnerability Type: DoS 
CWE ID: CWE-399
Summary: The vhost_dev_ioctl function in drivers/vhost/vhost.c in the Linux kernel before 4.1.5 allows local users to cause a denial of service (memory consumption) via a VHOST_SET_LOG_FD ioctl call that triggers permanent file-descriptor allocation.
Commit Message: vhost: actually track log eventfd file

While reviewing vhost log code, I found out that log_file is never
set. Note: I haven't tested the change (QEMU doesn't use LOG_FD yet).

Cc: stable@vger.kernel.org
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>