linux-kernel - Re: [PATCH] neighbour: Fix __randomize

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Message-ID: <a6dc78b1-8ae4-4530-acf6-2931e1863e77@embeddedor.com>
Date:   Mon, 27 Nov 2023 19:33:40 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Joey Gouly <joey.gouly@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Bill Wendling <morbo@...gle.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] neighbour: Fix __randomize_layout crash in struct
 neighbour



On 11/27/23 18:29, Kees Cook wrote:
> On Sat, Nov 25, 2023 at 03:33:58PM -0600, Gustavo A. R. Silva wrote:
>> Previously, one-element and zero-length arrays were treated as true
>> flexible arrays, even though they are actually "fake" flex arrays.
>> The __randomize_layout would leave them untouched at the end of the
>> struct, similarly to proper C99 flex-array members.
>>
>> However, this approach changed with commit 1ee60356c2dc ("gcc-plugins:
>> randstruct: Only warn about true flexible arrays"). Now, only C99
>> flexible-array members will remain untouched at the end of the struct,
>> while one-element and zero-length arrays will be subject to randomization.
>>
>> Fix a `__randomize_layout` crash in `struct neighbour` by transforming
>> zero-length array `primary_key` into a proper C99 flexible-array member.
>>
>> Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays")
>> Closes: https://lore.kernel.org/linux-hardening/20231124102458.GB1503258@e124191.cambridge.arm.com/
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> 
> Yes, please. Do we have any other 0-sized arrays hiding out in the
> kernel? We need to get these all cleared...

I've found 27 instances of zero-length fake-flex arrays in next-20231127.

I'll send a patch series to transform all of them.

> 
> Reviewed-by: Kees Cook <keescook@...omium.org>
> 

Thanks!
--
Gustavo