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

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Date:   Mon, 23 Aug 2021 19:55:20 +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
Subject: Re: [RESEND][PATCH] virtio_console: protect max_nr_ports to avoid
 invalid value

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@...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);