linux-kernel - [PATCH 2/2] virtio_console: protect max_nr

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Date:   Fri, 20 Aug 2021 15:41:56 +0800
From:   Xianting Tian <xianting.tian@...ux.alibaba.com>
To:     amit@...nel.org, arnd@...db.de, gregkh@...uxfoundation.org
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Xianting Tian <xianting.tian@...ux.alibaba.com>
Subject: [PATCH 2/2] virtio_console: protect max_nr_ports to avoid invalid value

In theory untrusted remote host can pass a big or overflow value
of max_nr_ports to guest, it may cause guest system consumes
a lot of memory when create vqs and other impacts.

Add the protection to guarantee max_nr_ports to get a safa value.

Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
---
 drivers/char/virtio_console.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 7eaf303a7..bba985c81 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -29,6 +29,8 @@
 
 #define is_rproc_enabled IS_ENABLED(CONFIG_REMOTEPROC)
 
+#define MAX_NR_PORTS	MAX_NR_HVC_CONSOLES
+
 /*
  * This is a global struct for storing common data for all the devices
  * this driver handles.
@@ -2039,6 +2041,9 @@ static int virtcons_probe(struct virtio_device *vdev)
 		multiport = true;
 	}
 
+	/* limit max_nr_ports to avoid invalid value from untrusted remote host */
+	portdev->max_nr_ports = min_t(u32, portdev->max_nr_ports, MAX_NR_PORTS);
+
 	err = init_vqs(portdev);
 	if (err < 0) {
 		dev_err(&vdev->dev, "Error %d initializing vqs\n", err);
-- 
2.17.1