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From: Kees Cook <keescook@chromium.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: "Mickaël Salaün" <mic@digikod.net>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Aleksa Sarai" <cyphar@cyphar.com>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Mimi Zohar" <zohar@linux.ibm.com>,
	"Stephen Smalley" <stephen.smalley.work@gmail.com>,
	"Christian Heimes" <christian@python.org>,
	"Deven Bowers" <deven.desai@linux.microsoft.com>,
	"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
	"John Johansen" <john.johansen@canonical.com>,
	"Kentaro Takeda" <takedakn@nttdata.co.jp>,
	"Lev R. Oshvang ." <levonshe@gmail.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Eric Chiang" <ericchiang@google.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>,
	"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>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-integrity@vger.kernel.org,
	"LSM List" <linux-security-module@vger.kernel.org>,
	"Linux FS Devel" <linux-fsdevel@vger.kernel.org>
Subject: Re: How about just O_EXEC? (was Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC)
Date: Fri, 15 May 2020 08:50:16 -0700
Message-ID: <202005150847.2B1ED8F81@keescook> (raw)
In-Reply-To: <87r1vluuli.fsf@oldenburg2.str.redhat.com>

On Fri, May 15, 2020 at 04:43:37PM +0200, Florian Weimer wrote:
> * Kees Cook:
> 
> > On Fri, May 15, 2020 at 10:43:34AM +0200, Florian Weimer wrote:
> >> * Kees Cook:
> >> 
> >> > Maybe I've missed some earlier discussion that ruled this out, but I
> >> > couldn't find it: let's just add O_EXEC and be done with it. It actually
> >> > makes the execve() path more like openat2() and is much cleaner after
> >> > a little refactoring. Here are the results, though I haven't emailed it
> >> > yet since I still want to do some more testing:
> >> > https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=kspp/o_exec/v1
> >> 
> >> I think POSIX specifies O_EXEC in such a way that it does not confer
> >> read permissions.  This seems incompatible with what we are trying to
> >> achieve here.
> >
> > I was trying to retain this behavior, since we already make this
> > distinction between execve() and uselib() with the MAY_* flags:
> >
> > execve():
> >         struct open_flags open_exec_flags = {
> >                 .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
> >                 .acc_mode = MAY_EXEC,
> >
> > uselib():
> >         static const struct open_flags uselib_flags = {
> >                 .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
> >                 .acc_mode = MAY_READ | MAY_EXEC,
> >
> > I tried to retain this in my proposal, in the O_EXEC does not imply
> > MAY_READ:
> 
> That doesn't quite parse for me, sorry.
> 
> The point is that the script interpreter actually needs to *read* those
> files in order to execute them.

I think I misunderstood what you meant (Mickaël got me sorted out
now). If O_EXEC is already meant to be "EXEC and _not_ READ nor WRITE",
then yes, this new flag can't be O_EXEC. I was reading the glibc
documentation (which treats it as a permission bit flag, not POSIX,
which treats it as a complete mode description).

-- 
Kees Cook

  reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 15:31 [PATCH v5 0/6] Add support for O_MAYEXEC 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 [this message]
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
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

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