Re: [PATCH v1 1/6] virtio console: Harden multiport against invalid host input

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>, Arnd Bergmann <arnd@arndb.de>,
	Amit Shah <amit@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	elena.reshetova@intel.com, kirill.shutemov@linux.intel.com
Subject: Re: [PATCH v1 1/6] virtio console: Harden multiport against invalid host input
Date: Fri, 20 Jan 2023 08:01:53 -0500	[thread overview]
Message-ID: <20230120080130-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20230119135721.83345-2-alexander.shishkin@linux.intel.com>

On Thu, Jan 19, 2023 at 03:57:16PM +0200, Alexander Shishkin wrote:
> From: Andi Kleen <ak@linux.intel.com>
> 
> It's possible for the host to set the multiport flag, but pass in
> 0 multiports, which results in:
> 
> BUG: KASAN: slab-out-of-bounds in init_vqs+0x244/0x6c0 drivers/char/virtio_console.c:1878
> Write of size 8 at addr ffff888001cc24a0 by task swapper/1
> 
> CPU: 0 PID: 1 Comm: swapper Not tainted 5.15.0-rc1-140273-gaab0bb9fbaa1-dirty #588
> Call Trace:
>  init_vqs+0x244/0x6c0 drivers/char/virtio_console.c:1878
>  virtcons_probe+0x1a3/0x5b0 drivers/char/virtio_console.c:2042
>  virtio_dev_probe+0x2b9/0x500 drivers/virtio/virtio.c:263
>  call_driver_probe drivers/base/dd.c:515
>  really_probe+0x1c9/0x5b0 drivers/base/dd.c:601
>  really_probe_debug drivers/base/dd.c:694
>  __driver_probe_device+0x10d/0x1f0 drivers/base/dd.c:754
>  driver_probe_device+0x68/0x150 drivers/base/dd.c:786
>  __driver_attach+0xca/0x200 drivers/base/dd.c:1145
>  bus_for_each_dev+0x108/0x190 drivers/base/bus.c:301
>  driver_attach+0x30/0x40 drivers/base/dd.c:1162
>  bus_add_driver+0x325/0x3c0 drivers/base/bus.c:618
>  driver_register+0xf3/0x1d0 drivers/base/driver.c:171
> ...
> 
> Add a suitable sanity check.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Amit Shah <amit@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/char/virtio_console.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 6a821118d553..f4fd5fe7cd3a 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1843,6 +1843,9 @@ static int init_vqs(struct ports_device *portdev)
>  	int err;
>  
>  	nr_ports = portdev->max_nr_ports;
> +	if (use_multiport(portdev) && nr_ports < 1)
> +		return -EINVAL;
> +
>  	nr_queues = use_multiport(portdev) ? (nr_ports + 1) * 2 : 2;
>  
>  	vqs = kmalloc_array(nr_queues, sizeof(struct virtqueue *), GFP_KERNEL);

Weird.  Don't we already check for that?

        /* Don't test MULTIPORT at all if we're rproc: not a valid feature! */
        if (!is_rproc_serial(vdev) &&
            virtio_cread_feature(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
                                 struct virtio_console_config, max_nr_ports,
                                 &portdev->max_nr_ports) == 0) {
                if (portdev->max_nr_ports == 0 ||
                    portdev->max_nr_ports > VIRTCONS_MAX_PORTS) {
                        dev_err(&vdev->dev,
                                "Invalidate max_nr_ports %d",
                                portdev->max_nr_ports);
                        err = -EINVAL;
                        goto free;
                }
                multiport = true;
        }

> -- 
> 2.39.0

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