linux-hardening - Re: [PATCH 19/64] ip: Use struct

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Message-ID: <45855f4f-f7cf-b7b3-bcd6-c9ebc3a55c64@acm.org>
Date:   Wed, 28 Jul 2021 18:59:08 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH 19/64] ip: Use struct_group() for memcpy() regions

On 7/28/21 2:01 PM, Kees Cook wrote:
> On Wed, Jul 28, 2021 at 07:55:53AM +0200, Greg Kroah-Hartman wrote:
>>>  struct ethhdr {
>>> -	unsigned char	h_dest[ETH_ALEN];	/* destination eth addr	*/
>>> -	unsigned char	h_source[ETH_ALEN];	/* source ether addr	*/
>>> +	union {
>>> +		struct {
>>> +			unsigned char h_dest[ETH_ALEN];	  /* destination eth addr */
>>> +			unsigned char h_source[ETH_ALEN]; /* source ether addr	  */
>>> +		};
>>> +		struct {
>>> +			unsigned char h_dest[ETH_ALEN];	  /* destination eth addr */
>>> +			unsigned char h_source[ETH_ALEN]; /* source ether addr	  */
>>> +		} addrs;
>>
>> A union of the same fields in the same structure in the same way?
>>
>> Ah, because struct_group() can not be used here?  Still feels odd to see
>> in a userspace-visible header.
> 
> Yeah, there is some inconsistency here. I will clean this up for v2.
> 
> Is there a place we can put kernel-specific macros for use in UAPI
> headers? (I need to figure out where things like __kernel_size_t get
> defined...)

How about using two memset() calls to clear h_dest[] and h_source[]
instead of modifying the uapi header?

Thanks,

Bart.