linux-kernel - Re: [PATCH] ksys_mount: check for permissions before resource allocation

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Message-Id: <BD48252B-65D7-4238-BDA2-71BAC1CEA855@gmail.com>
Date:   Tue, 5 Jun 2018 10:59:51 +0400
From:   Ilya Matveychikov <matvejchikov@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] ksys_mount: check for permissions before resource
 allocation

Just CC’ed to some of maintainers.

$ perl scripts/get_maintainer.pl fs/0001-ksys_mount-check-for-permissions-before-resource-all.patch
Alexander Viro <viro@...iv.linux.org.uk> (maintainer:FILESYSTEMS (VFS and infrastructure))
linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS and infrastructure))
linux-kernel@...r.kernel.org (open list)

> On Jun 5, 2018, at 6:00 AM, Ilya Matveychikov <matvejchikov@...il.com> wrote:
> 
> Early check for mount permissions prevents possible allocation of 3
> pages from kmalloc() pool by unpriveledged user which can be used for
> spraying the kernel heap.
> 
> Signed-off-by: Ilya V. Matveychikov <matvejchikov@...il.com>
> ---
> fs/namespace.c | 3 +++
> 1 file changed, 3 insertions(+)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 5f75969adff1..1ef8feb2de2a 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -3046,6 +3046,9 @@ int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,
> 	char *kernel_dev;
> 	void *options;
> 
> +	if (!may_mount())
> +		return -EPERM;
> +
> 	kernel_type = copy_mount_string(type);
> 	ret = PTR_ERR(kernel_type);
> 	if (IS_ERR(kernel_type))
> --
> 2.17.0
>