linux-hardening - Re: [PATCH] kheaders: Use array declaration instead of char

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Date:   Fri, 3 Mar 2023 16:19:51 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Joel Fernandes <joel@...lfernandes.org>,
        Jakub Kicinski <kuba@...nel.org>, <stable@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH] kheaders: Use array declaration instead of char

From: Kees Cook <keescook@...omium.org>
Date: Thu,  2 Mar 2023 14:49:50 -0800

> Under CONFIG_FORTIFY_SOURCE, memcpy() will check the size of destination
> and source buffers. Defining kernel_headers_data as "char" would trip
> this check. Since these addresses are treated as byte arrays, define
> them as arrays (as done everywhere else).

Yet another array-as-one-char, I wonder how many are still here...

> 
> This was seen with:
> 
>   $ cat /sys/kernel/kheaders.tar.xz >> /dev/null
> 
>   detected buffer overflow in memcpy
>   kernel BUG at lib/string_helpers.c:1027!
>   ...
>   RIP: 0010:fortify_panic+0xf/0x20
>   [...]
>   Call Trace:
>    <TASK>
>    ikheaders_read+0x45/0x50 [kheaders]
>    kernfs_fop_read_iter+0x1a4/0x2f0
>   ...
> 
> Reported-by: Jakub Kicinski <kuba@...nel.org>
> Link: https://lore.kernel.org/bpf/20230302112130.6e402a98@kernel.org/
> Tested-by: Jakub Kicinski <kuba@...nel.org>
> Fixes: 43d8ce9d65a5 ("Provide in-kernel headers to make extending kernel easier")
> Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
> Cc: stable@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>

> ---
>  kernel/kheaders.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
[...]

Thanks,
Olek