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Date:   Mon, 27 Nov 2023 19:33:40 -0600
From:   "Gustavo A. R. Silva" <>
To:     Kees Cook <>,
        "Gustavo A. R. Silva" <>
Cc:     Joey Gouly <>,
        "David S. Miller" <>,
        Eric Dumazet <>,
        Jakub Kicinski <>,
        Paolo Abeni <>,
        Bill Wendling <>,,,
Subject: Re: [PATCH] neighbour: Fix __randomize_layout crash in struct

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:
>> Signed-off-by: Gustavo A. R. Silva <>
> 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 <>


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