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Date:   Mon, 27 Nov 2023 16:29:25 -0800
From:   Kees Cook <keescook@chromium.org>
To:     "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc:     Joey Gouly <joey.gouly@arm.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Bill Wendling <morbo@google.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] neighbour: Fix __randomize_layout crash in struct
 neighbour
Message-ID: <202311271628.E5EED48@keescook>
References: <ZWJoRsJGnCPdJ3+2@work>
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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@kernel.org>

Yes, please. Do we have any other 0-sized arrays hiding out in the
kernel? We need to get these all cleared...

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

-- 
Kees Cook