From: "Enderborg, Peter" <Peter.Enderborg@sony.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Rafael J . Wysocki" <rafael@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jonathan Corbet <corbet@lwn.net>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
Randy Dunlap <rdunlap@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH 2/2] debugfs: Add access restriction option
Date: Wed, 15 Jul 2020 10:59:12 +0000 [thread overview]
Message-ID: <45741a2f-3763-a41d-62ad-29b5fbb16101@sony.com> (raw)
In-Reply-To: <20200715103532.GB2876510@kroah.com>
On 7/15/20 12:35 PM, Greg Kroah-Hartman wrote:
> On Wed, Jul 15, 2020 at 10:03:19AM +0000, Enderborg, Peter wrote:
>> On 7/15/20 11:39 AM, Greg Kroah-Hartman wrote:
>>> On Wed, Jul 15, 2020 at 10:42:07AM +0200, Peter Enderborg wrote:
>>>> Since debugfs include sensitive information it need to be treated
>>>> carefully. But it also has many very useful debug functions for userspace.
>>>> With this option we can have same configuration for system with
>>>> need of debugfs and a way to turn it off. This gives a extra protection
>>>> for exposure on systems where user-space services with system
>>>> access are attacked.
>>>>
>>>> It is controlled by a configurable default value that can be override
>>>> with a kernel command line parameter. (debugfs=)
>>>>
>>>> It can be on or off, but also internally on but not seen from user-space.
>>>> This no-fs mode do not register a debugfs as filesystem, but client can
>>>> register their parts in the internal structures. This data can be readed
>>>> with a debugger or saved with a crashkernel. When it is off clients
>>>> get EPERM error when accessing the functions for registering their
>>>> components.
>>>>
>>>> Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
>>>> ---
>>>> .../admin-guide/kernel-parameters.txt | 14 +++++++
>>>> fs/debugfs/inode.c | 37 +++++++++++++++++++
>>>> fs/debugfs/internal.h | 14 +++++++
>>>> lib/Kconfig.debug | 32 ++++++++++++++++
>>>> 4 files changed, 97 insertions(+)
>>>>
>>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>>> index fb95fad81c79..805aa2e58491 100644
>>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>>> @@ -827,6 +827,20 @@
>>>> useful to also enable the page_owner functionality.
>>>> on: enable the feature
>>>>
>>>> + debugfs= [KNL] This parameter enables what is exposed to userspace
>>>> + and debugfs internal clients.
>>>> + Format: { on, no-fs, off }
>>>> + on: All functions are enabled.
>>>> + no-fs: Filesystem is not registered but kernel clients can
>>>> + access APIs and a crashkernel can be used to read
>>>> + its content. There is nothing to mount.
>>>> + off: Filesystem is not registered and clients
>>>> + get a -EPERM as result when trying to register files
>>>> + or directories within debugfs.
>>>> + This is equilivant of the runtime functionality if
>>>> + debugfs was not enabled in the kernel at all.
>>>> + Default value is set in build-time with a kernel configuration.
>>> Naming is hard. In looking at this, should "no-fs" be called
>>> "no-mount"? That's a better description of what it does, right?
>> I think no-fs cover it better since it does not register a filesystem
>> but provides the interfaces. Mounting is then indirectly stopped.
> But "mounting" is the common term we all know. "no-fs" doesn't really
> describe what is happening here, right? Everything works internally
> just fine, but we just are forbidding the filesystem to be mounted.
>
I have no objection but now you know the background. So no-mount then.
I will do a new patch-set.
>> The idea start with a check for mounting but it is much more
>> definitely stopped by prevention of register of the filesystem.
>> I can imagine to have a forth "mode" where it register a fs but
>> not allowing mounting. Such mode maybe useful for some runtime
>> configuration. But this patch is about boot time configuration.
> Preventing the registering of the filesystem does cut out the ability to
> mount the thing quite well :)
>
> We could change it to just prevent the superblock from mounting if you
> want, as maybe we do need the fs to remain in the list of filesystems in
> the kernel at that point in time? Otherwise we are lying to userspace.
It is all about hide it away for userspace.
> thanks,
>
> greg k-h
next prev parent reply other threads:[~2020-07-15 11:47 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-17 13:37 [PATCH v3] debugfs: Add access restriction option Peter Enderborg
2020-06-17 14:15 ` Greg Kroah-Hartman
2020-06-17 14:39 ` Enderborg, Peter
2020-06-17 15:10 ` Randy Dunlap
2020-06-22 8:30 ` [PATCH v4 0/2] " Peter Enderborg
2020-06-22 8:30 ` [PATCH 1/2] tracefs: Remove unnecessary debug_fs checks Peter Enderborg
2020-06-22 9:18 ` Greg Kroah-Hartman
2020-06-22 13:47 ` Steven Rostedt
2020-06-22 8:30 ` [PATCH 2/2] debugfs: Add access restriction option Peter Enderborg
2020-07-10 13:06 ` Greg Kroah-Hartman
2020-07-15 8:42 ` [PATCH v5 0/2] " Peter Enderborg
2020-07-15 8:42 ` [PATCH 1/2] tracefs: Remove unnecessary debug_fs checks Peter Enderborg
2020-07-15 8:42 ` [PATCH 2/2] debugfs: Add access restriction option Peter Enderborg
2020-07-15 9:39 ` Greg Kroah-Hartman
2020-07-15 10:03 ` Enderborg, Peter
2020-07-15 10:35 ` Greg Kroah-Hartman
2020-07-15 10:59 ` Enderborg, Peter [this message]
2020-07-21 6:47 ` Enderborg, Peter
2020-07-15 15:25 ` [PATCH v6 0/2] " Peter Enderborg
2020-07-15 15:25 ` [PATCH 1/2] tracefs: Remove unnecessary debug_fs checks Peter Enderborg
2020-07-15 15:25 ` [PATCH 2/2] debugfs: Add access restriction option Peter Enderborg
2020-07-16 3:30 ` Randy Dunlap
2020-07-16 4:54 ` [PATCH v7 0/2] " Peter Enderborg
2020-07-16 4:54 ` [PATCH 1/2] tracefs: Remove unnecessary debug_fs checks Peter Enderborg
2020-07-16 4:54 ` [PATCH 2/2] debugfs: Add access restriction option Peter Enderborg
2020-07-16 5:12 ` Randy Dunlap
2020-07-16 7:15 ` [PATCH v8 0/2] " Peter Enderborg
2020-07-16 7:15 ` [PATCH 1/2] tracefs: Remove unnecessary debug_fs checks Peter Enderborg
2020-07-16 7:15 ` [PATCH 2/2] debugfs: Add access restriction option Peter Enderborg
2020-07-16 15:26 ` Randy Dunlap
2020-07-23 15:11 ` [PATCH v8 0/2] " Greg Kroah-Hartman
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=45741a2f-3763-a41d-62ad-29b5fbb16101@sony.com \
--to=peter.enderborg@sony.com \
--cc=akpm@linux-foundation.org \
--cc=corbet@lwn.net \
--cc=gregkh@linuxfoundation.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=rafael@kernel.org \
--cc=rdunlap@infradead.org \
--cc=rostedt@goodmis.org \
/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).