[RESEND][PATCH] virtio_console: protect max_nr_ports to avoid invalid value

[RESEND][PATCH] virtio_console: protect max_nr_ports to avoid invalid value

[Xianting Tian]

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 safe value.

Signed-off-by: Xianting Tian <xianting.tian@linux.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

Re: [RESEND][PATCH] virtio_console: protect max_nr_ports to avoid invalid value

[Xianting TIan]

Could I get comments for the patch? thanks

Is the value of  MAX_NR_PORTS accurate?

this fix is similar to below patches, which are megered recently,

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14-rc7&id=63947b3434f475418b9677a393d025c0962c2cf8 
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14-rc7&id=63947b3434f475418b9677a393d025c0962c2cf8>

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14-rc7&id=82e89ea077b93b3c131fa175b0df3acb5b1d5cdf 
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14-rc7&id=82e89ea077b93b3c131fa175b0df3acb5b1d5cdf>

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14-rc7&id=d00d8da5869a2608e97cfede094dfc5e11462a46 
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14-rc7&id=d00d8da5869a2608e97cfede094dfc5e11462a46>


在 2021/8/20 下午3:52, Xianting Tian 写道:
> 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 safe value.
>
> Signed-off-by: Xianting Tian <xianting.tian@linux.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);

Re: [RESEND][PATCH] virtio_console: protect max_nr_ports to avoid invalid value

[Greg KH]

On Fri, Aug 20, 2021 at 03:52:19PM +0800, Xianting Tian wrote:
> 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.

How can you have a untrusted host?  Can't they do a lot worse things
than just this?

> 
> Add the protection to guarantee max_nr_ports to get a safe value.
> 
> Signed-off-by: Xianting Tian <xianting.tian@linux.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

How was this value picked?

thanks,

greg k-h