linux-kernel - Re: RFC: capabilities(7): notes for kernel developers

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Message-ID: <20161216201026.GB14856@mail.hallyn.com>
Date:   Fri, 16 Dec 2016 14:10:26 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Casey Schaufler <casey@...aufler-ca.com>,
        John Stultz <john.stultz@...aro.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jann Horn <jann@...jh.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-man <linux-man@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: RFC: capabilities(7): notes for kernel developers

Quoting Michael Kerrisk (man-pages) (mtk.manpages@...il.com):
> On 12/16/2016 01:44 AM, Casey Schaufler wrote:
> > On 12/15/2016 4:31 PM, John Stultz wrote:
> >> On Thu, Dec 15, 2016 at 12:40 PM, Casey Schaufler
> >> <casey@...aufler-ca.com> wrote:
> >>> On 12/15/2016 11:41 AM, Michael Kerrisk (man-pages) wrote:
> >>>> On 12/15/2016 05:29 PM, Casey Schaufler wrote:
> >>>>> CAP_WAKE_ALARM could readily be CAP_TIME.
> >>>> Actually, I don't quite understand what you mean with that sentence.
> >>>> Could you elaborate?
> >>> Should have said CAP_SYS_TIME
> >>>
> >>> Setting an alarm could be considered a time management function,
> >>> depending on what it actually does.
> >> Just a nit here. CAP_WAKE_ALARM is more about the privilege of waking
> >> a system from suspend, while CAP_SYS_TIME covers the ability to set
> >> the time. One wouldn't necessarily want to give applications which
> >> could wake a system up the capability to also set the time.
> > 
> > Doesn't really matter, except that an ignorant developer
> > might make the mistake I did and assume that WAKE_ALARM
> > was somehow related to time management. If you want to use
> > it as an example don't let my dunderheadedness get in your
> > way.
> 
> Actually, I decided it wasn't such a good example anyway.
> That capability could potentially be generic. (But it probably
> should better have been named something like 'CAP_WAKE_SYSTEM'.)

How about:

Subject: [PATCH 1/1] capabilities: alias CAP_WAKE_SYSTEM to CAP_WAKE_ALARM

As suggested by Michael Kerrisk his is a less confusing name, and
this won't break any old userspace.

Signed-off-by: Serge Hallyn <serge@...lyn.com>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
---
 include/uapi/linux/capability.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
index fd4f87d..ba972ff 100644
--- a/include/uapi/linux/capability.h
+++ b/include/uapi/linux/capability.h
@@ -357,6 +357,8 @@ struct vfs_ns_cap_data {
 
 #define CAP_WAKE_ALARM            35
 
+#define CAP_WAKE_SYSTEM      CAP_WAKE_ALARM
+
 /* Allow preventing system suspends */
 
 #define CAP_BLOCK_SUSPEND    36
-- 
2.7.4