From: Daniel Colascione <dancol@google.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Tim Murray <timmurray@google.com>,
Joel Fernandes <joelaf@google.com>,
Suren Baghdasaryan <surenb@google.com>,
Kees Cook <keescook@chromium.org>,
Christian Brauner <christian.brauner@canonical.com>
Subject: Re: [RFC PATCH] Implement /proc/pid/kill
Date: Wed, 31 Oct 2018 15:16:32 +0000 [thread overview]
Message-ID: <CAKOZues0_jMfW8xAa0mC=QS7UnHMzkWb5nCz3S_GDf3RzPg90Q@mail.gmail.com> (raw)
In-Reply-To: <20181031151007.GA21207@redhat.com>
On Wed, Oct 31, 2018 at 3:10 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> On 10/31, Daniel Colascione wrote:
>>
>> > perhaps it would be simpler to do
>> >
>> > my_cred = override_creds(file->f_cred);
>> > kill_pid(...);
>> > revert_creds(my_cred);
>>
>> Thanks for the suggestion. That looks neat, but it's not quite enough.
>> The problem is that check_kill_permission looks for
>> same_thread_group(current, t) _before_ checking kill_of_by_cred,
>
> Yes, you are right.
>
> Looks like kill_pid_info_as_cred() can find another user, but probably
> it needs some changes with or without /proc/pid/kill ...
>
>> There's another problem though: say we open /proc/pid/5/kill *, with
>> proc 5 being an ordinary unprivileged process, e.g., the shell. At
>> open(2) time, the access check passes. Now suppose PID 5 execve(2)s
>> into a setuid process. The kill FD is still open, so the kill FD's
>> holder can send a signal
>
> Confused... why? kill_ok_by_cred() should fail?
Not if we don't run it. :-) I thought you were proposing that we do
*all* access checks in open() and let write() succeed unconditionally,
since that's the model that a lot of FD-mediated resources (like
regular files) use. (MAC notwithstanding.)
Anyway, I sent a v2 patch that I think closes the hole another way. In
v2, we just require that the real user ID that opens a /proc/pid/kill
file is the same one that writes to it. It successfully blocks the
setuid attack above while preserving all the write-time permission
checks and keeping the close correspondence between
write()-on-proc-pid-kill-fd and kill(2). Can you think of any
situation where this scheme breaks? I *think* comparing struct user
addresses instead of numeric UIDs will protect the check against user
namespace shenanigans.
next prev parent reply other threads:[~2018-10-31 15:16 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 22:10 [RFC PATCH] Implement /proc/pid/kill Daniel Colascione
2018-10-30 3:21 ` Joel Fernandes
2018-10-30 8:50 ` Daniel Colascione
2018-10-30 10:39 ` Christian Brauner
2018-10-30 10:40 ` Christian Brauner
2018-10-30 10:48 ` Daniel Colascione
2018-10-30 11:04 ` Christian Brauner
2018-10-30 11:12 ` Daniel Colascione
2018-10-30 11:19 ` Christian Brauner
2018-10-31 5:00 ` Eric W. Biederman
2018-10-30 17:01 ` Joel Fernandes
2018-10-30 5:00 ` Aleksa Sarai
2018-10-30 9:05 ` Daniel Colascione
2018-10-30 20:45 ` Aleksa Sarai
2018-10-30 21:42 ` Joel Fernandes
2018-10-30 22:23 ` Aleksa Sarai
2018-10-30 22:33 ` Joel Fernandes
2018-10-30 22:49 ` Aleksa Sarai
2018-10-31 0:42 ` Joel Fernandes
2018-10-31 1:59 ` Daniel Colascione
2018-10-30 23:10 ` Daniel Colascione
2018-10-30 23:23 ` Christian Brauner
2018-10-30 23:55 ` Daniel Colascione
2018-10-31 2:56 ` Aleksa Sarai
2018-10-31 4:24 ` Joel Fernandes
2018-11-01 20:40 ` Joel Fernandes
2018-11-02 9:46 ` Christian Brauner
2018-11-02 14:34 ` Serge E. Hallyn
2018-10-31 0:57 ` Joel Fernandes
2018-10-31 1:56 ` Daniel Colascione
2018-10-31 4:47 ` Eric W. Biederman
2018-10-31 4:44 ` Eric W. Biederman
2018-10-31 12:44 ` Oleg Nesterov
2018-10-31 13:27 ` Daniel Colascione
2018-10-31 15:10 ` Oleg Nesterov
2018-10-31 15:16 ` Daniel Colascione [this message]
2018-10-31 15:49 ` Oleg Nesterov
2018-11-01 11:53 ` David Laight
2018-11-01 15:50 ` Daniel Colascione
2018-10-31 14:37 ` [PATCH v2] " Daniel Colascione
2018-10-31 15:05 ` Joel Fernandes
2018-10-31 17:33 ` Aleksa Sarai
2018-10-31 21:47 ` Joel Fernandes
2018-10-31 15:59 ` [PATCH v3] " Daniel Colascione
2018-10-31 17:54 ` Tycho Andersen
2018-10-31 18:00 ` Daniel Colascione
2018-10-31 18:17 ` Tycho Andersen
2018-10-31 19:33 ` Daniel Colascione
2018-10-31 20:06 ` Tycho Andersen
2018-11-01 11:33 ` David Laight
2018-11-12 1:19 ` Eric W. Biederman
2018-10-31 16:22 ` [RFC PATCH] " Jann Horn
2018-11-01 4:53 ` Andy Lutomirski
2018-11-12 23:13 ` Pavel Machek
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