From: Andrew Lutomirski <luto@mit.edu>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Jamie Lokier <jamie@shareable.org>,
Will Drewry <wad@chromium.org>,
linux-kernel@vger.kernel.org, keescook@chromium.org,
john.johansen@canonical.com, serge.hallyn@canonical.com,
coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com,
djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org,
jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com,
penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, mingo@elte.hu,
akpm@linux-foundation.org, khilman@ti.com,
borislav.petkov@amd.com, amwang@redhat.com, oleg@redhat.com,
ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de,
dhowells@redhat.com, daniel.lezcano@free.fr,
linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, olofj@chromium.org,
mhalcrow@google.com, dlaor@redhat.com, corbet@lwn.net,
alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch
Date: Sun, 15 Jan 2012 14:07:32 -0800 [thread overview]
Message-ID: <CAObL_7F4hEvdyJLNhodOOETTv-Dur8gEadLkzESQWFC2C57t7w@mail.gmail.com> (raw)
In-Reply-To: <4F1345DB.8040303@schaufler-ca.com>
On Sun, Jan 15, 2012 at 1:32 PM, Casey Schaufler <casey@schaufler-ca.com> wrote:
> On 1/15/2012 12:59 PM, Andrew Lutomirski wrote:
>>
>> On Sun, Jan 15, 2012 at 12:16 PM, Casey Schaufler
>> <casey@schaufler-ca.com> wrote:
>>>
>>> On 1/14/2012 12:22 PM, Linus Torvalds wrote:
>>>>
>>>> And yes, I really seriously do believe that is both safer and simpler
>>>> than some model that says "you can drop stuff", and then you have to
>>>> start making up rules for what "dropping" means.
>>>>
>>>> Does "dropping" mean allowing setuid(geteuid()) for example? That *is*
>>>> dropping the uid in a _POSIX_SAVED_IDS environment. And I'm saying
>>>> that no, we should not even allow that. It's simply all too "subtle".
>>>
>>>
>>> I am casting my two cents worth behind Linus. Dropping
>>> privilege can be every bit as dangerous as granting privilege
>>> in the real world of atrocious user land code. Especially in
>>> the case of security policy enforcing user land code.
>>
>> Can you think of *any* plausible attack that is possible with my patch
>> (i.e. no_new_privs allows setuid, setresuid, and capset) that would be
>> prevented or even mitigated if I blocked those syscalls? I can't.
>> (The sendmail-style attack is impossible with no_new_privs.)
>
>
> I am notoriously bad at coming up with this sort of example.
> I will try, I may not hit the mark, but it should be close.
>
> The application is running with saved uid != euid when
> no-new-privs is set. It execs a new binary, which keeps
> the saved and effective uids. The program calls setreuid,
> which succeeds. It opens the saved userid's files.
If you don't trust that binary, then why are you execing it with saved
uid != euid in the first place? If you are setting no_new_privs, then
you are new code and should have at least some basic awareness of the
semantics. The exact same "exploit" is possible if you have
CAP_DAC_OVERRIDE with either no_new_privs semantics -- if you have a
privilege and you run untrusted code, then you had better remove that
privilege somehow for the untrusted code.
IOW, *drop privileges if you are a sandbox*. Otherwise you're screwed
with or without no_new_privs.
Another way of saying this is: no_new_privs is not a sandbox. It's
just a way to make it safe for sandboxes and other such weird things
processes can do to themselves safe across execve. If you want a
sandbox, use seccomp mode 2, which will require you to set
no_new_privs.
--Andy
next prev parent reply other threads:[~2012-01-15 22:07 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-12 23:38 [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch Will Drewry
2012-01-12 23:38 ` [PATCH v3 2/3] seccomp_filters: system call filtering using BPF Will Drewry
2012-01-13 0:51 ` Randy Dunlap
2012-01-12 23:59 ` Will Drewry
2012-01-13 1:35 ` Randy Dunlap
2012-01-13 17:39 ` Eric Paris
2012-01-13 18:50 ` Will Drewry
2012-01-12 23:38 ` [PATCH v3 3/3] Documentation: prctl/seccomp_filter Will Drewry
2012-01-15 1:52 ` Randy Dunlap
2012-01-16 1:41 ` Will Drewry
2012-01-17 23:29 ` Eric Paris
2012-01-17 23:54 ` Will Drewry
2012-01-12 23:47 ` [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch Linus Torvalds
2012-01-13 0:03 ` Will Drewry
2012-01-13 0:42 ` Andrew Lutomirski
2012-01-13 0:57 ` Linus Torvalds
2012-01-13 1:11 ` Andrew Lutomirski
2012-01-13 1:17 ` Linus Torvalds
2012-01-14 13:30 ` Jamie Lokier
2012-01-14 19:21 ` Will Drewry
2012-01-14 20:22 ` Linus Torvalds
2012-01-14 21:04 ` Andrew Lutomirski
2012-01-15 20:16 ` Casey Schaufler
2012-01-15 20:59 ` Andrew Lutomirski
2012-01-15 21:32 ` Casey Schaufler
2012-01-15 22:07 ` Andrew Lutomirski [this message]
2012-01-16 2:04 ` Will Drewry
2012-01-18 3:12 ` Eric W. Biederman
2012-01-16 2:41 ` Casey Schaufler
2012-01-16 7:45 ` Andrew Lutomirski
2012-01-16 18:02 ` Casey Schaufler
2012-01-13 1:37 ` Will Drewry
2012-01-13 1:41 ` Andrew Lutomirski
2012-01-13 2:09 ` 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=CAObL_7F4hEvdyJLNhodOOETTv-Dur8gEadLkzESQWFC2C57t7w@mail.gmail.com \
--to=luto@mit.edu \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=alan@lxorguk.ukuu.org.uk \
--cc=amwang@redhat.com \
--cc=avi@redhat.com \
--cc=borislav.petkov@amd.com \
--cc=casey@schaufler-ca.com \
--cc=corbet@lwn.net \
--cc=coreyb@linux.vnet.ibm.com \
--cc=daniel.lezcano@free.fr \
--cc=dhowells@redhat.com \
--cc=djm@mindrot.org \
--cc=dlaor@redhat.com \
--cc=eparis@redhat.com \
--cc=eric.dumazet@gmail.com \
--cc=gregkh@suse.de \
--cc=jamie@shareable.org \
--cc=jmorris@namei.org \
--cc=john.johansen@canonical.com \
--cc=keescook@chromium.org \
--cc=khilman@ti.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=mhalcrow@google.com \
--cc=mingo@elte.hu \
--cc=oleg@redhat.com \
--cc=olofj@chromium.org \
--cc=penberg@cs.helsinki.fi \
--cc=pmoore@redhat.com \
--cc=rostedt@goodmis.org \
--cc=scarybeasts@gmail.com \
--cc=segoon@openwall.com \
--cc=serge.hallyn@canonical.com \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
--cc=wad@chromium.org \
/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).