linux-kernel - Re: [PATCH v2] capabilities.7, prctl.2: Document ambient capabilities

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Date:	Tue, 29 Sep 2015 10:57:43 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Andrew Morton <akpm@...uxfoundation.org>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	"Ted Ts'o" <tytso@....edu>, "Andrew G. Morgan" <morgan@...nel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Aaron Jones <aaronmdjones@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Markku Savela <msa@...h.iki.fi>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v2] capabilities.7, prctl.2: Document ambient capabilities

On Tue, Sep 29, 2015 at 10:49 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Sep 29, 2015 at 10:47 AM, Kees Cook <keescook@...omium.org> wrote:
>> On Mon, Sep 28, 2015 at 6:03 PM, Andy Lutomirski <luto@...nel.org> wrote:
>>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>>> ---
>>>  man2/prctl.2        | 12 ++++++++++++
>>>  man7/capabilities.7 | 40 ++++++++++++++++++++++++++++++++++------
>>>  2 files changed, 46 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/man2/prctl.2 b/man2/prctl.2
>>> index e743a6305969..5bcec391c110 100644
>>> --- a/man2/prctl.2
>>> +++ b/man2/prctl.2
>>> @@ -954,6 +954,18 @@ had been called.
>>>  For further information on Intel MPX, see the kernel source file
>>>  .IR Documentation/x86/intel_mpx.txt .
>>>  .\"
>>> +.TP
>>> +.BR PR_CAP_AMBIENT " (since Linux 4.2)"
>>> +Reads or changes the ambient capability set.  If arg2 is PR_CAP_AMBIENT_RAISE,
>>> +then the capability specified in arg3 is added to the ambient set.  This will
>>> +fail, returning EPERM, if the capability is not already both permitted and
>>> +inheritable or if the SECBIT_NO_CAP_AMBIENT_RAISE securebit is set.  If arg2
>>> +is PR_CAP_AMBIENT_LOWER, then the capability specified in arg3 is removed
>>> +from the ambient set.  If arg2 is PR_CAP_AMBIENT_IS_SET, then
>>> +.BR prctl (2)
>>> +will return 1 if the capability in arg3 is in the ambient set and 0 if not.
>>> +If arg2 is PR_CAP_AMBIENT_CLEAR_ALL, then all capabilities will
>>> +be removed from the ambient set.
>>
>> In the case of CLEAR_ALL, is arg3 "don't care", or must it be set to 0?
>
> Must be zero.

Okay, cool. Probably that should be noted here.

-Kees

-- 
Kees Cook
Chrome OS Security
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