Linux-Security-Module Archive on lore.kernel.org
 help / color / Atom feed
From: "Mickaël Salaün" <mic@digikod.net>
To: David Laight <David.Laight@ACULAB.COM>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "Aleksa Sarai" <cyphar@cyphar.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Christian Heimes" <christian@python.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Deven Bowers" <deven.desai@linux.microsoft.com>,
	"Eric Chiang" <ericchiang@google.com>,
	"Florian Weimer" <fweimer@redhat.com>,
	"James Morris" <jmorris@namei.org>, "Jan Kara" <jack@suse.cz>,
	"Jann Horn" <jannh@google.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Kees Cook" <keescook@chromium.org>,
	"Lakshmi Ramasubramanian" <nramas@linux.microsoft.com>,
	"Matthew Garrett" <mjg59@google.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
	"Mimi Zohar" <zohar@linux.ibm.com>,
	"Philippe Trébuchet" <philippe.trebuchet@ssi.gouv.fr>,
	"Scott Shell" <scottsh@microsoft.com>,
	"Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Steve Dower" <steve.dower@python.org>,
	"Steve Grubb" <sgrubb@redhat.com>,
	"Thibaut Sautereau" <thibaut.sautereau@ssi.gouv.fr>,
	"Vincent Strubel" <vincent.strubel@ssi.gouv.fr>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"linux-security-module@vger.kernel.org"
	<linux-security-module@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v5 0/6] Add support for O_MAYEXEC
Date: Thu, 7 May 2020 11:30:02 +0200
Message-ID: <64426377-7fc4-6f37-7371-2e2a584e3032@digikod.net> (raw)
In-Reply-To: <ad28ab5fe7854b41a575656e95b4da17@AcuMS.aculab.com>


On 07/05/2020 11:00, David Laight wrote:
> From: Mickaël Salaün
>> Sent: 07 May 2020 09:37
> ...
>>> None of that description actually says what the patch actually does.
>>
>> "Add support for O_MAYEXEC" "to enable to control script execution".
>> What is not clear here? This seems well understood by other commenters.
>> The documentation patch and the talks can also help.
> 
> I'm guessing that passing O_MAYEXEC to open() requests the kernel
> check for execute 'x' permissions (as well as read).

Yes, but only with openat2().

> 
> Then kernel policy determines whether 'read' access is actually enough,
> or whether 'x' access (possibly masked by mount permissions) is needed.
> 
> If that is true, two lines say what is does.

The "A simple system-wide security policy" paragraph introduce that, but
I'll highlight it in the next cover letter. The most important point is
to understand why it is required, before getting to how it will be
implemented.

> 
> Have you ever set a shell script permissions to --x--s--x ?
> Ends up being executable by everyone except the owner!

In this case the script is indeed executable but it can't be executed
because the interpreter (i.e. the user) needs to be able to read the
file. Of course, if the user has CAP_DAC_OVERRIDE (like the root user),
read is still allowed.

> Having the kernel pass all '#!' files to their interpreters
> through an open fd might help security.

This is interesting but it doesn't address the current issue: being able
to have a consistent (script) executability system policy. Maybe its
this point of view which wasn't clear enough?

> In that case the user doesn't need read access to the file
> in order to get an interpreter to process it.

Yes, but this brings security issues, because the interpreter (i.e. the
user) would then be able to read files without read permission.

> (You'd need to stop strace showing the contents to actually
> hide them.)

It doesn't matter if the process is traced or not, the kernel handles
impersonation scopes thanks to ptrace_may_access().

  reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 15:31 Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 1/6] fs: Add support for an O_MAYEXEC flag on openat2(2) Mickaël Salaün
2020-05-12 21:05   ` Kees Cook
2020-05-12 21:40     ` Christian Heimes
2020-05-12 22:56       ` Kees Cook
2020-05-13 10:13     ` Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 2/6] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount property Mickaël Salaün
2020-05-12 21:09   ` Kees Cook
2020-05-14  8:14     ` Lev R. Oshvang .
2020-05-14 15:48       ` Kees Cook
2020-05-17 16:57         ` Lev R. Oshvang .
2020-05-05 15:31 ` [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2020-05-05 15:44   ` Randy Dunlap
2020-05-05 16:55     ` Mickaël Salaün
2020-05-05 17:40       ` Randy Dunlap
2020-05-12 21:48   ` Kees Cook
2020-05-13 11:09     ` Mickaël Salaün
2020-05-13 15:37   ` Stephen Smalley
2020-05-13 23:27     ` Kees Cook
2020-05-14  3:05       ` Kees Cook
2020-05-14 10:12         ` David Laight
2020-05-14 12:22         ` Stephen Smalley
2020-05-14 14:41           ` Kees Cook
2020-05-14 15:52             ` Stephen Smalley
2020-05-14 15:45           ` Kees Cook
2020-05-14 16:10             ` Stephen Smalley
2020-05-14 19:16               ` Mickaël Salaün
2020-05-15  0:58                 ` Tetsuo Handa
2020-05-15  8:01                 ` How about just O_EXEC? (was Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC) Kees Cook
2020-05-15  8:43                   ` Florian Weimer
2020-05-15 14:37                     ` Kees Cook
2020-05-15 14:43                       ` Florian Weimer
2020-05-15 15:50                         ` Kees Cook
2020-05-18  7:26                           ` Florian Weimer
2020-05-19  2:23                           ` Aleksa Sarai
2020-05-19 10:13                             ` Mickaël Salaün
2020-05-15 11:04                   ` Mickaël Salaün
2020-05-15 15:46                     ` Kees Cook
2020-05-15 18:24                       ` Mickaël Salaün
2020-05-14 19:21       ` [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 4/6] selftest/openat2: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2020-05-12 21:57   ` Kees Cook
2020-05-13 11:18     ` Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 5/6] doc: Add documentation for the fs.open_mayexec_enforce sysctl Mickaël Salaün
2020-05-12 22:00   ` Kees Cook
2020-05-13 11:20     ` Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 6/6] ima: add policy support for the new file open MAY_OPENEXEC flag Mickaël Salaün
2020-05-05 15:36 ` [PATCH v5 0/6] Add support for O_MAYEXEC Mickaël Salaün
2020-05-06 13:58   ` Lev R. Oshvang .
2020-05-06 15:41     ` Aleksa Sarai
2020-05-07  8:30     ` Mickaël Salaün
2020-05-07  8:05 ` David Laight
2020-05-07  8:36   ` Mickaël Salaün
2020-05-07  9:00     ` David Laight
2020-05-07  9:30       ` Mickaël Salaün [this message]
2020-05-07  9:44         ` David Laight
2020-05-07 13:38           ` Mickaël Salaün
2020-05-08  7:15             ` Lev R. Oshvang .
2020-05-08 14:01               ` Mimi Zohar

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=64426377-7fc4-6f37-7371-2e2a584e3032@digikod.net \
    --to=mic@digikod.net \
    --cc=David.Laight@ACULAB.COM \
    --cc=ast@kernel.org \
    --cc=christian@python.org \
    --cc=corbet@lwn.net \
    --cc=cyphar@cyphar.com \
    --cc=daniel@iogearbox.net \
    --cc=deven.desai@linux.microsoft.com \
    --cc=ericchiang@google.com \
    --cc=fweimer@redhat.com \
    --cc=jack@suse.cz \
    --cc=jannh@google.com \
    --cc=jmorris@namei.org \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-integrity@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=mickael.salaun@ssi.gouv.fr \
    --cc=mjg59@google.com \
    --cc=mtk.manpages@gmail.com \
    --cc=nramas@linux.microsoft.com \
    --cc=philippe.trebuchet@ssi.gouv.fr \
    --cc=scottsh@microsoft.com \
    --cc=sean.j.christopherson@intel.com \
    --cc=sgrubb@redhat.com \
    --cc=shuah@kernel.org \
    --cc=steve.dower@python.org \
    --cc=thibaut.sautereau@ssi.gouv.fr \
    --cc=vincent.strubel@ssi.gouv.fr \
    --cc=viro@zeniv.linux.org.uk \
    --cc=willy@infradead.org \
    --cc=zohar@linux.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

Linux-Security-Module Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-security-module/0 linux-security-module/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-security-module linux-security-module/ https://lore.kernel.org/linux-security-module \
		linux-security-module@vger.kernel.org
	public-inbox-index linux-security-module

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-security-module


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git