From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: mtk.manpages@gmail.com, Jann Horn <jann@thejh.net>,
James Morris <jmorris@namei.org>,
linux-man <linux-man@vger.kernel.org>,
Stephen Smalley <sds@tycho.nsa.gov>,
lkml <linux-kernel@vger.kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
linux-security-module <linux-security-module@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: Documenting ptrace access mode checking
Date: Thu, 23 Jun 2016 09:02:26 +0200 [thread overview]
Message-ID: <465c5a45-f807-3124-2735-f8e18e96b503@gmail.com> (raw)
In-Reply-To: <CAGXu5j+DoWCT=NwZK-yNBmZOu9LdEn=0-gjJvtPVmNJFanWoKA@mail.gmail.com>
On 06/22/2016 11:11 PM, Kees Cook wrote:
> On Wed, Jun 22, 2016 at 12:21 PM, Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
>> On 06/21/2016 10:55 PM, Jann Horn wrote:
>>> On Tue, Jun 21, 2016 at 11:41:16AM +0200, Michael Kerrisk (man-pages)
>>> wrote:
>>>> 5. The kernel LSM security_ptrace_access_check() interface is
>>>> invoked to see if ptrace access is permitted. The results
>>>> depend on the LSM. The implementation of this interface in
>>>> the default LSM performs the following steps:
>>>
>>>
>>> For people who are unaware of how the LSM API works, it might be good to
>>> clarify that the commoncap LSM is *always* invoked; otherwise, it might
>>> give the impression that using another LSM would replace it.
>>
>>
>> As we can see, I am one of those who are unaware of how the LSM API
>> works :-/.
>>
>>> (Also, are there other documents that refer to it as "default LSM"? I
>>> think that that term is slightly confusing.)
>>
>>
>> No, that's a terminological confusion of my own making. Fixed now.
>>
>> I changed this text to:
>>
>> Various parts of the kernel-user-space API (not just ptrace(2)
>> operations), require so-called "ptrace access mode permissions"
>> which are gated by any enabled Linux Security Module (LSMs)—for
>> example, SELinux, Yama, or Smack—and by the the commoncap LSM
>> (which is always invoked). Prior to Linux 2.6.27, all such
>> checks were of a single type. Since Linux 2.6.27, two access
>> mode levels are distinguished:
>>
>> BTW, can you point me at the piece(s) of kernel code that show that
>> "commoncap" is always invoked in addition to any other LSM that has
>> been installed?
>
> It's not entirely obvious, but the bottom of security/commoncap.c shows:
Thanks Kees!
Cheers,
Michael
>
> #ifdef CONFIG_SECURITY
>
> struct security_hook_list capability_hooks[] = {
> LSM_HOOK_INIT(capable, cap_capable),
> ...
> };
>
> void __init capability_add_hooks(void)
> {
> security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks));
> }
>
> #endif
>
> And security/security.c shows the initialization order of the LSMs:
>
> int __init security_init(void)
> {
> pr_info("Security Framework initialized\n");
>
> /*
> * Load minor LSMs, with the capability module always first.
> */
> capability_add_hooks();
> yama_add_hooks();
> loadpin_add_hooks();
>
> /*
> * Load all the remaining security modules.
> */
> do_security_initcalls();
>
> return 0;
> }
>
>
> -Kees
>
>
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2016-06-23 7:02 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-21 9:41 Documenting ptrace access mode checking Michael Kerrisk (man-pages)
2016-06-21 19:55 ` Eric W. Biederman
2016-06-21 20:29 ` Kees Cook
2016-06-21 20:58 ` Eric W. Biederman
2016-06-22 19:20 ` Michael Kerrisk (man-pages)
2016-06-22 19:20 ` Michael Kerrisk (man-pages)
2016-06-23 19:04 ` Eric W. Biederman
2016-06-24 9:57 ` Michael Kerrisk (man-pages)
2016-06-22 21:51 ` Oleg Nesterov
2016-06-23 7:06 ` Michael Kerrisk (man-pages)
2016-06-23 18:56 ` Eric W. Biederman
2016-06-24 8:18 ` Michael Kerrisk (man-pages)
2016-06-21 20:55 ` Jann Horn
2016-06-22 19:21 ` Michael Kerrisk (man-pages)
2016-06-22 21:11 ` Kees Cook
2016-06-23 7:02 ` Michael Kerrisk (man-pages) [this message]
2016-06-24 8:40 ` Michael Kerrisk (man-pages)
2016-06-24 15:18 ` Casey Schaufler
2016-06-24 20:07 ` Kees Cook
2016-06-25 7:21 ` Michael Kerrisk (man-pages)
2016-06-22 22:44 ` Jann Horn
2016-06-23 7:42 ` Michael Kerrisk (man-pages)
2016-06-24 6:35 ` Jann Horn
2016-06-23 18:05 ` Stephen Smalley
2016-06-24 8:33 ` Michael Kerrisk (man-pages)
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