linux-kernel - Re: [RESEND][PATCH] virtio_console: protect max_nr

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Message-ID: <YSippdinb67QYU6K@kroah.com>
Date:   Fri, 27 Aug 2021 11:00:21 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Xianting Tian <xianting.tian@...ux.alibaba.com>
Cc:     amit@...nel.org, arnd@...db.de,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND][PATCH] virtio_console: protect max_nr_ports to avoid
 invalid value

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@...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

How was this value picked?

thanks,

greg k-h