From: Kees Cook <keescook@chromium.org>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: "Thibaut Sautereau" <thibaut.sautereau@clip-os.org>,
linux-kernel@vger.kernel.org, "Aleksa Sarai" <cyphar@cyphar.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Christian Heimes" <christian@python.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Deven Bowers" <deven.desai@linux.microsoft.com>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Eric Biggers" <ebiggers@kernel.org>,
"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>,
"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>,
"Tetsuo Handa" <penguin-kernel@i-love.sakura.ne.jp>,
"Thibaut Sautereau" <thibaut.sautereau@ssi.gouv.fr>,
"Vincent Strubel" <vincent.strubel@ssi.gouv.fr>,
kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 5/7] fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC
Date: Wed, 22 Jul 2020 12:40:19 -0700 [thread overview]
Message-ID: <202007221239.E00125F019@keescook> (raw)
In-Reply-To: <efb88aab-f9f9-4b66-e7ab-3aa054eec96e@digikod.net>
On Wed, Jul 22, 2020 at 09:04:28PM +0200, Mickaël Salaün wrote:
>
> On 22/07/2020 18:16, Thibaut Sautereau wrote:
> > On Thu, Jul 16, 2020 at 04:39:14PM +0200, Mickaël Salaün wrote:
> >>
> >> On 15/07/2020 22:37, Kees Cook wrote:
> >>> On Tue, Jul 14, 2020 at 08:16:36PM +0200, Mickaël Salaün wrote:
> >>>> @@ -2849,7 +2855,7 @@ static int may_open(const struct path *path, int acc_mode, int flag)
> >>>> case S_IFLNK:
> >>>> return -ELOOP;
> >>>> case S_IFDIR:
> >>>> - if (acc_mode & (MAY_WRITE | MAY_EXEC))
> >>>> + if (acc_mode & (MAY_WRITE | MAY_EXEC | MAY_OPENEXEC))
> >>>> return -EISDIR;
> >>>> break;
> >>>
> >>> (I need to figure out where "open for reading" rejects S_IFDIR, since
> >>> it's clearly not here...)
> >
> > Doesn't it come from generic_read_dir() in fs/libfs.c?
> >
> >>>
> >>>> case S_IFBLK:
> >>>> @@ -2859,13 +2865,26 @@ static int may_open(const struct path *path, int acc_mode, int flag)
> >>>> fallthrough;
> >>>> case S_IFIFO:
> >>>> case S_IFSOCK:
> >>>> - if (acc_mode & MAY_EXEC)
> >>>> + if (acc_mode & (MAY_EXEC | MAY_OPENEXEC))
> >>>> return -EACCES;
> >>>> flag &= ~O_TRUNC;
> >>>> break;
> >>>
> >>> This will immediately break a system that runs code with MAY_OPENEXEC
> >>> set but reads from a block, char, fifo, or socket, even in the case of
> >>> a sysadmin leaving the "file" sysctl disabled.
> >>
> >> As documented, O_MAYEXEC is for regular files. The only legitimate use
> >> case seems to be with pipes, which should probably be allowed when
> >> enforcement is disabled.
> >
> > By the way Kees, while we fix that for the next series, do you think it
> > would be relevant, at least for the sake of clarity, to add a
> > WARN_ON_ONCE(acc_mode & MAY_OPENEXEC) for the S_IFSOCK case, since a
> > socket cannot be open anyway?
If it's a state that userspace should never be able to reach, then yes,
I think a WARN_ON_ONCE() would be nice.
> We just did some more tests (for the next patch series) and it turns out
> that may_open() can return EACCES before another part returns ENXIO.
>
> As a reminder, the next series will deny access to block devices,
> character devices, fifo and socket when opened with O_MAYEXEC *and* if
> any policy is enforced (via the sysctl).
>
> The question is then: do we prefer to return EACCES when a policy is
> enforced (on a socket), or do we stick to the ENXIO? The EACCES approach
> will be more consistent with devices and fifo handling, and seems safer
> (belt and suspenders) thought.
I think EACCES is correct for these cases, since it's a new flag, etc.
--
Kees Cook
next prev parent reply other threads:[~2020-07-22 19:40 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-14 18:16 [PATCH v6 0/7] Add support for O_MAYEXEC Mickaël Salaün
2020-07-14 18:16 ` [PATCH v6 1/7] exec: Change uselib(2) IS_SREG() failure to EACCES Mickaël Salaün
2020-07-14 18:16 ` [PATCH v6 2/7] exec: Move S_ISREG() check earlier Mickaël Salaün
2020-07-14 18:16 ` [PATCH v6 3/7] exec: Move path_noexec() " Mickaël Salaün
2020-07-14 18:16 ` [PATCH v6 4/7] fs: Introduce O_MAYEXEC flag for openat2(2) Mickaël Salaün
2020-07-15 20:06 ` Kees Cook
2020-07-16 14:18 ` Mickaël Salaün
2020-07-16 15:31 ` Kees Cook
2020-07-14 18:16 ` [PATCH v6 5/7] fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2020-07-14 18:40 ` Randy Dunlap
2020-07-16 14:40 ` Mickaël Salaün
2020-07-15 20:37 ` Kees Cook
2020-07-16 14:39 ` Mickaël Salaün
2020-07-22 16:16 ` Thibaut Sautereau
2020-07-22 19:04 ` Mickaël Salaün
2020-07-22 19:40 ` Kees Cook [this message]
2020-07-14 18:16 ` [PATCH v6 6/7] selftest/openat2: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2020-07-15 20:38 ` Kees Cook
2020-07-14 18:16 ` [PATCH v6 7/7] ima: add policy support for the new file open MAY_OPENEXEC flag Mickaël Salaün
2020-07-15 20:40 ` Kees Cook
2020-07-16 14:40 ` Mickaël Salaün
2020-07-16 14:59 ` Randy Dunlap
2020-07-16 15:22 ` Mickaël Salaün
2020-07-16 19:13 ` Kees Cook
2020-07-16 19:12 ` Kees Cook
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=202007221239.E00125F019@keescook \
--to=keescook@chromium.org \
--cc=akpm@linux-foundation.org \
--cc=ast@kernel.org \
--cc=christian.brauner@ubuntu.com \
--cc=christian@python.org \
--cc=corbet@lwn.net \
--cc=cyphar@cyphar.com \
--cc=daniel@iogearbox.net \
--cc=deven.desai@linux.microsoft.com \
--cc=dvyukov@google.com \
--cc=ebiggers@kernel.org \
--cc=ericchiang@google.com \
--cc=fweimer@redhat.com \
--cc=jack@suse.cz \
--cc=jannh@google.com \
--cc=jmorris@namei.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=mic@digikod.net \
--cc=mickael.salaun@ssi.gouv.fr \
--cc=mjg59@google.com \
--cc=mtk.manpages@gmail.com \
--cc=nramas@linux.microsoft.com \
--cc=penguin-kernel@i-love.sakura.ne.jp \
--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@clip-os.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
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).