From: Thomas-Mich Richter <tmricht@linux.ibm.com>
To: Kees Cook <keescook@chromium.org>, Greg KH <gregkh@linuxfoundation.org>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>,
brueckner@linux.vnet.ibm.com,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] inode: debugfs_create_dir uses mode permission from parent
Date: Wed, 2 May 2018 09:16:29 +0200 [thread overview]
Message-ID: <8d3e702b-470a-542e-4e0d-6a3c58419f0f@linux.ibm.com> (raw)
In-Reply-To: <CAGXu5j+LK8-g9bg+RNn+-v1LpRC32sTCAUNZr1v0HXquiG9fQw@mail.gmail.com>
On 04/27/2018 04:58 PM, Kees Cook wrote:
> On Fri, Apr 27, 2018 at 6:49 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> I'm going to add Kees and the kernel-hardning list here, as I'd like
>> their opinions for the patch below.
>>
>> Kees, do you have any problems with this patch? I know you worked on
>> making debugfs more "secure" from non-root users, this should still keep
>> the intial mount permissions all fine, right? Anything I'm not
>> considering here?
>
> This appears correct to me. I'd like to see some stronger rationale
> for why this is needed, just so I have a "design" to compare the
> implementation against. :)
>
> Normally, the top-level directory permissions should block all the
> subdirectories too. The only time I think of this being needed is if
> someone is explicitly bind-mounting a subdirectory to another location
> (e.g. Chrome OS does this for the i915 subdirectory). In that case,
> I'd expect them to tweak permissions too. Thomas, what's your
> use-case?
>
> -Kees
>
There is no 'real use case'. I wrote the patch because of discussions
regarding file permissions for files located deeply in the
directory tree, for example
-r--r--r-- 1 root root 0 Apr 27 14:23 /sys/kernel/debug/kprobes/blacklist
which gives the impression it is world readable.
This happened to me in recent discussions when I wrote patches to fix some
of the address randomized output of /sys files which broke the perf tool.
During discussion people often forgot that the root /sys/kernel/debug is rwx for
root only and blocks non root access to subdirectories and files. They simply
looked at the file permissions.
I have not thougth about the bind-mount case nor did I test this scenario.
--
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
next prev parent reply other threads:[~2018-05-02 7:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-27 12:35 [PATCH v2] debugfs: inode: debugfs_create_dir uses mode permission from parent Thomas Richter
2018-04-27 13:49 ` [PATCH v2] " Greg KH
2018-04-27 14:58 ` Kees Cook
2018-05-02 7:16 ` Thomas-Mich Richter [this message]
2018-05-02 14:29 ` Kees Cook
2018-04-30 14:15 ` Jann Horn
2018-04-30 14:26 ` Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=8d3e702b-470a-542e-4e0d-6a3c58419f0f@linux.ibm.com \
--to=tmricht@linux.ibm.com \
--cc=brueckner@linux.vnet.ibm.com \
--cc=gregkh@linuxfoundation.org \
--cc=heiko.carstens@de.ibm.com \
--cc=keescook@chromium.org \
--cc=kernel-hardening@lists.openwall.com \
--cc=linux-kernel@vger.kernel.org \
--cc=schwidefsky@de.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).