linux-kernel - Re: [PATCH] ia64: validate user arguments in csum_partial_copy_from

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Message-ID: <alpine.LRH.2.02.1402071100050.14709@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Fri, 7 Feb 2014 11:05:08 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>
cc:	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	David Miller <davem@...emloft.net>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] ia64: validate user arguments in
 csum_partial_copy_from_user

It actually turns out that the check in csum_partial_copy_from_user is 
pointless (the check is already done in csum_and_copy_from_user that is 
the only caller of csum_partial_copy_from_user).

So, please ignore this patch - we need to clean up alpha and x86 
implementation of csum_partial_copy_from_user and not add this pointless 
check to ia64.

Mikulas


On Thu, 23 Jan 2014, Mikulas Patocka wrote:

> ia64: validate user arguments in csum_partial_copy_from_user
> 
> csum_partial_copy_from_user needs to validate that the argument points to
> userspace and not kernelspace (see for example commit
> 3ddc5b46a8e90f3c9251338b60191d0a804b0d92). Consequently, we need to use
> copy_from_user instead of __copy_from_user.
> 
> We also need to change csum_partial_copy_nocheck - this function is called
> with src pointing to kernel space, so we call set_fs(KERNEL_DS) to prevent
> copy_from_user from failing.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> Cc: stable@...r.kernel.org
> 
> ---
>  arch/ia64/lib/csum_partial_copy.c |   17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6-ia64/arch/ia64/lib/csum_partial_copy.c
> ===================================================================
> --- linux-2.6-ia64.orig/arch/ia64/lib/csum_partial_copy.c	2014-01-24 02:40:10.000000000 +0100
> +++ linux-2.6-ia64/arch/ia64/lib/csum_partial_copy.c	2014-01-24 03:05:26.000000000 +0100
> @@ -116,8 +116,12 @@ csum_partial_copy_from_user(const void _
>  	 * scared.
>  	 */
>  
> -	if (__copy_from_user(dst, src, len) != 0 && errp)
> -		*errp = -EFAULT;
> +	if (copy_from_user(dst, src, len) != 0) {
> +		if (*errp)
> +			*errp = -EFAULT;
> +		memset(dst, 0, len);
> +		return psum;
> +	}
>  
>  	result = do_csum(dst, len);
>  
> @@ -133,8 +137,13 @@ EXPORT_SYMBOL(csum_partial_copy_from_use
>  __wsum
>  csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
>  {
> -	return csum_partial_copy_from_user((__force const void __user *)src,
> -					   dst, len, sum, NULL);
> +	__wsum checksum;
> +	mm_segment_t oldfs = get_fs();
> +	set_fs(KERNEL_DS);
> +	checksum = csum_partial_copy_from_user((__force const void __user *)src,
> +					       dst, len, sum, NULL);
> +	set_fs(oldfs);
> +	return checksum;
>  }
>  
>  EXPORT_SYMBOL(csum_partial_copy_nocheck);
> 
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