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From: Jann Horn <jannh@google.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>,
	Andy Lutomirski <luto@kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Jeff Layton <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Christian Brauner <christian@brauner.io>,
	Tycho Andersen <tycho@tycho.ws>,
	David Drysdale <drysdale@google.com>,
	Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>,
	Aleksa Sarai <asarai@suse.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	containers@lists.linux-foundation.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters
Date: Fri, 10 May 2019 22:10:32 +0200
Message-ID: <20190510201032.GA253532@google.com> (raw)
In-Reply-To: <87o94d6aql.fsf@xmission.com>

On Tue, May 07, 2019 at 07:38:58PM -0500, Eric W. Biederman wrote:
> Jann Horn <jannh@google.com> writes:
> > In my opinion, CVE-2019-5736 points out two different problems:
> >
> > The big problem: The __ptrace_may_access() logic has a special-case
> > short-circuit for "introspection" that you can't opt out of;
> 
> Once upon a time in a galaxy far far away I fixed a bug where we missing
> ptrace_may_access checks on various proc files and systems using selinux
> stopped working.  At the time selinux did not allow ptrace like access
> to yourself.  The "introspection" special case was the quick and simple
> work-around.
> 
> There is nothing fundamental in having the "introspection" special case
> except that various lsms have probably grown to depend upon it being
> there.  I expect without difficulty we could move the check down
> into the various lsms.  Which would get that check out of the core
> kernel code.

Oh, if that's an option, that would be great, I think.


But this means, for example, that a non-root, non-dumpable process can't
open /proc/self/maps anymore, or open /proc/self/fd/*, and things like
that, without making itself dumpable. I would be surprised if there is
no code out there that relies on that.

From what I can tell, without the introspection special case,
introspection would fail in the following cases (assuming that the
process is not capable and isn't using sys_setfs[ug]id()):

 - ruid/euid/suid are not all the same
 - rgid/egid/sgid are not all the same
 - process is not dumpable

I think that there probably should be some way for a non-dumpable
process to look at its own procfs entries? If we could start from a
clean slate, I'd propose an opt-in flag to openat() for that, but
since we don't have a clean slate, I'd be afraid of breaking things
with that. But maybe I'm just being overly careful here?

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-06 16:54 [PATCH v6 0/6] namei: resolveat(2) path resolution restriction API Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 1/6] namei: split out nd->dfd handling to dirfd_path_init Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 2/6] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 3/6] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 4/6] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-05-06 16:54 ` [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters Aleksa Sarai
2019-05-06 18:37   ` Jann Horn
2019-05-06 19:17     ` Aleksa Sarai
2019-05-06 23:41       ` Andy Lutomirski
2019-05-08  0:54       ` Aleksa Sarai
2019-05-10 20:41       ` Jann Horn
2019-05-10 21:20         ` Andy Lutomirski
2019-05-10 22:55           ` Jann Horn
2019-05-10 23:36             ` Christian Brauner
2019-05-11 15:49               ` Aleksa Sarai
2019-05-11 17:00             ` Andy Lutomirski
2019-05-11 17:21               ` Linus Torvalds
2019-05-11 17:26                 ` Linus Torvalds
2019-05-11 17:31                   ` Aleksa Sarai
2019-05-11 17:43                     ` Linus Torvalds
2019-05-11 17:48                       ` Christian Brauner
2019-05-11 18:00                       ` Aleksa Sarai
2019-05-11 22:39                 ` Andy Lutomirski
     [not found]                   ` <CAHk-=wg3+3GfHsHdB4o78jNiPh_5ShrzxBuTN-Y8EZfiFMhCvw@mail.gmail.com>
2019-05-12 10:19                     ` Christian Brauner
     [not found]                     ` <9CD2B97D-A6BD-43BE-9040-B410D996A195@amacapital.net>
2019-05-12 10:44                       ` Linus Torvalds
2019-05-12 13:35                         ` Aleksa Sarai
2019-05-12 13:38                           ` Aleksa Sarai
2019-05-12 14:34                           ` Andy Lutomirski
2019-05-11 17:26               ` Aleksa Sarai
2019-05-08  0:38     ` Eric W. Biederman
2019-05-10 20:10       ` Jann Horn [this message]
2019-05-06 16:54 ` [PATCH v6 6/6] namei: resolveat(2) syscall Aleksa Sarai

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