Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Paul Moore <paul@paul-moore.com>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: "Adrian Reber" <areber@redhat.com>,
	"Christian Brauner" <christian.brauner@ubuntu.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>,
	"Nicolas Viennot" <Nicolas.Viennot@twosigma.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-kernel@vger.kernel.org, selinux@vger.kernel.org,
	"Eric Paris" <eparis@parisplace.org>,
	"Jann Horn" <jannh@google.com>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v4 3/3] prctl: Allow ptrace capable processes to change /proc/self/exe
Date: Thu, 2 Jul 2020 18:00:10 -0400
Message-ID: <CAHC9VhQZ=cwiOay6OMMdM1UHm69wDaga9HBkyTbx8-1OU=aBvA@mail.gmail.com> (raw)
In-Reply-To: <20200702211647.GB3283@mail.hallyn.com>

On Thu, Jul 2, 2020 at 5:16 PM Serge E. Hallyn <serge@hallyn.com> wrote:
> On Wed, Jul 01, 2020 at 08:49:06AM +0200, Adrian Reber wrote:
> > From: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
> >
> > Previously, the current process could only change the /proc/self/exe
> > link with local CAP_SYS_ADMIN.
> > This commit relaxes this restriction by permitting such change with
> > CAP_CHECKPOINT_RESTORE, and the ability to use ptrace.
> >
> > With access to ptrace facilities, a process can do the following: fork a
> > child, execve() the target executable, and have the child use ptrace()
> > to replace the memory content of the current process. This technique
> > makes it possible to masquerade an arbitrary program as any executable,
> > even setuid ones.
> >
> > Signed-off-by: Nicolas Viennot <Nicolas.Viennot@twosigma.com>
> > Signed-off-by: Adrian Reber <areber@redhat.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.

-- 
paul moore
www.paul-moore.com

  reply index

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 [this message]
2020-07-06 17:13       ` Nicolas Viennot
2020-07-06 17:44         ` Christian Brauner
2020-07-07 15:45           ` Christian Brauner
2020-07-07 20:27             ` Cyrill Gorcunov

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='CAHC9VhQZ=cwiOay6OMMdM1UHm69wDaga9HBkyTbx8-1OU=aBvA@mail.gmail.com' \
    --to=paul@paul-moore.com \
    --cc=0x7f454c46@gmail.com \
    --cc=Nicolas.Viennot@twosigma.com \
    --cc=areber@redhat.com \
    --cc=arnd@arndb.de \
    --cc=avagin@gmail.com \
    --cc=casey@schaufler-ca.com \
    --cc=chf@redhat.com \
    --cc=christian.brauner@ubuntu.com \
    --cc=dipeit@gmail.com \
    --cc=ebiederm@xmission.com \
    --cc=eparis@parisplace.org \
    --cc=gorcunov@openvz.org \
    --cc=jannh@google.com \
    --cc=kyurtsever@google.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=mclapinski@google.com \
    --cc=oleg@redhat.com \
    --cc=ovzxemul@gmail.com \
    --cc=rppt@linux.ibm.com \
    --cc=rstoyanov1@gmail.com \
    --cc=sargun@sargun.me \
    --cc=selinux@vger.kernel.org \
    --cc=serge@hallyn.com \
    --cc=stephen.smalley.work@gmail.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-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/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-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

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


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