linux-kernel - Re: [PATCH] procfs: block chmod on /proc/thread-self/comm

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Message-ID: <jjls2w5xh2urrkgxzts6jfwbpa2zpi3p6nsvjy7rpsum7rtt4c@4e5z735u4ofz>
Date:   Fri, 14 Jul 2023 00:06:02 +1000
From:   Aleksa Sarai <cyphar@...har.com>
To:     Willy Tarreau <w@....eu>
Cc:     Shuah Khan <shuah@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <brauner@...nel.org>,
        Dave Chinner <dchinner@...hat.com>,
        xu xin <cgel.zte@...il.com>, Al Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...kernel.io>,
        Zhihao Cheng <chengzhihao1@...wei.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Janis Danisevskis <jdanis@...gle.com>,
        Kees Cook <keescook@...omium.org>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Thomas Weißschuh <thomas@...ch.de>
Subject: Re: [PATCH] procfs: block chmod on /proc/thread-self/comm

On 2023-07-13, Willy Tarreau <w@....eu> wrote:
> +Cc Thomas Weißschuh <thomas@...ch.de> as this seems quite related to
> his finding about /proc/self/net:
> 
>   https://lore.kernel.org/lkml/20230624-proc-net-setattr-v1-0-73176812adee@weissschuh.net/#b

Yeah I saw this patch and (along with an earlier discussion with
Christian on the topic of chmod on symlinks -- see [1]) lead us to find
that there were three other cases where this happens unintentionally:

 * /proc/self (on the symlink itself)
 * /proc/thread-self (on the symlink itself)
 * /proc/thread-self/comm

The first two will be fixed by [1] so fixing them isn't necessary.

[1]: https://lore.kernel.org/linux-fsdevel/20230712-vfs-chmod-symlinks-v2-1-08cfb92b61dd@kernel.org/

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>