linux-kernel - Re: [PATCH V3 06/11] Restrict /dev/mem and /dev/kmem when module loading is restricted

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Date:	Wed, 4 Sep 2013 10:47:19 +1000 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Matthew Garrett <matthew.garrett@...ula.com>
cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	keescook@...omium.org, hpa@...or.com
Subject: Re: [PATCH V3 06/11] Restrict /dev/mem and /dev/kmem when module
 loading is restricted

On Tue, 3 Sep 2013, Matthew Garrett wrote:

> Allowing users to write to address space makes it possible for the kernel
> to be subverted, avoiding module loading restrictions. Prevent this when
> any restrictions have been imposed on loading modules.
> 
> Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>


Reviewed-by: James Morris <jmorris@...ei.org>



> ---
>  drivers/char/mem.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index 1af8664..61406c8 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -159,6 +159,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
>  	unsigned long copied;
>  	void *ptr;
>  
> +	if (secure_modules())
> +		return -EPERM;
> +
>  	if (!valid_phys_addr_range(p, count))
>  		return -EFAULT;
>  
> @@ -497,6 +500,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
>  	char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
>  	int err = 0;
>  
> +	if (secure_modules())
> +		return -EPERM;
> +
>  	if (p < (unsigned long) high_memory) {
>  		unsigned long to_write = min_t(unsigned long, count,
>  					       (unsigned long)high_memory - p);
> -- 
> 1.8.3.1
> 
> --
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-- 
James Morris
<jmorris@...ei.org>
--
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