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From: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
To: Paul Moore <paul@paul-moore.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Christian Brauner <christian.brauner@ubuntu.com>
Cc: "Adrian Reber" <areber@redhat.com>,
	"Eric Biederman" <ebiederm@xmission.com>,
	"Pavel Emelyanov" <ovzxemul@gmail.com>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Dmitry Safonov" <0x7f454c46@gmail.com>,
	"Andrei Vagin" <avagin@gmail.com>,
	"Michał Cłapiński" <mclapinski@google.com>,
	"Kamil Yurtsever" <kyurtsever@google.com>,
	"Dirk Petersen" <dipeit@gmail.com>,
	"Christine Flood" <chf@redhat.com>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Radostin Stoyanov" <rstoyanov1@gmail.com>,
	"Cyrill Gorcunov" <gorcunov@openvz.org>,
	"Stephen Smalley" <stephen.smalley.work@gmail.com>,
	"Sargun Dhillon" <sargun@sargun.me>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"linux-security-module@vger.kernel.org"
	<linux-security-module@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
	"Eric Paris" <eparis@parisplace.org>,
	"Jann Horn" <jannh@google.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: RE: [PATCH v4 3/3] prctl: Allow ptrace capable processes to change /proc/self/exe
Date: Mon, 6 Jul 2020 17:13:35 +0000	[thread overview]
Message-ID: <a2b4deacfc7541e3adea2f36a6f44262@EXMBDFT11.ad.twosigma.com> (raw)
In-Reply-To: <CAHC9VhQZ=cwiOay6OMMdM1UHm69wDaga9HBkyTbx8-1OU=aBvA@mail.gmail.com>

> > This is scary.  But I believe it is safe.
> >
> > Reviewed-by: Serge Hallyn <serge@hallyn.com>
> >
> > I am a bit curious about the implications of the selinux patch.
> > IIUC you are using the permission of the tracing process to execute
> > the file without transition, so this is a way to work around the
> > policy which might prevent the tracee from doing so.
> > Given that SELinux wants to be MAC, I'm not *quite* sure that's
> > considered kosher.  You also are skipping the PROCESS__PTRACE to
> > SECCLASS_PROCESS check which selinux_bprm_set_creds does later on.
> > Again I'm just not quite sure what's considered normal there these
> > days.
> >
> > Paul, do you have input there?
>
> I agree, the SELinux hook looks wrong.  Building on what Christian said, this looks more like a ptrace operation than an exec operation.

Serge, Paul, Christian,

I made a PoC to demonstrate the change of /proc/self/exe without CAP_SYS_ADMIN using only ptrace and execve.
You may find it here: https://github.com/nviennot/run_as_exe

What do you recommend to relax the security checks in the kernel when it comes to changing the exe link?

    Nico

  reply	other threads:[~2020-07-06 17:13 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-01  6:49 [PATCH v4 0/3] capabilities: Introduce CAP_CHECKPOINT_RESTORE Adrian Reber
2020-07-01  6:49 ` [PATCH v4 1/3] " Adrian Reber
2020-07-01  8:27   ` Christian Brauner
2020-07-03 11:11     ` Adrian Reber
2020-07-01  6:49 ` [PATCH v4 2/3] selftests: add clone3() CAP_CHECKPOINT_RESTORE test Adrian Reber
2020-07-02 20:53   ` Serge E. Hallyn
2020-07-03 11:18     ` Adrian Reber
2020-07-03 18:12       ` Serge E. Hallyn
2020-07-01  6:49 ` [PATCH v4 3/3] prctl: Allow ptrace capable processes to change /proc/self/exe Adrian Reber
2020-07-01  8:55   ` Christian Brauner
2020-07-02 21:58     ` Serge E. Hallyn
2020-07-02 21:16   ` Serge E. Hallyn
2020-07-02 22:00     ` Paul Moore
2020-07-06 17:13       ` Nicolas Viennot [this message]
2020-07-06 17:44         ` Christian Brauner
2020-07-07 15:45           ` Christian Brauner
2020-07-07 20:27             ` Cyrill Gorcunov

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