Re: [RFC] Capabilities still can't be inherited by normal programs

From: Andrew G. Morgan
Date: Sun Dec 02 2012 - 17:26:48 EST

On Sun, Dec 2, 2012 at 10:35 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Sun, Dec 2, 2012 at 9:21 AM, Andrew G. Morgan <morgan@xxxxxxxxxx> wrote:
>> There is a fairly well written paper ;-) explaining how things are
>> supposed to work:
>> The inheritable set is not intended to work the way you seem to want.
>> Naive inheritance like that is quite explicitly the opposite of what
>> was designed.
> I'm aware that the system was designed, or perhaps evolved, to prevent
> users with uid != 0 from inheriting capabilities unless vfs
> inheritable caps are granted on a per-file basis. I want a way around
> that -- I want to mix non-root, capabilities, and exec. This is damn
> near impossible right now if I don't have CAP_SETFCAP or root's
> explicit, per-program cooperation. CAP_SETFCAP is essentially
> equivalent to "let me do anything".
> As it stands, using something like pam_cap to grant a user cap_net_raw
> is useless -- that user can't use the privilege because (unless uid ==
> 0) the privilege will never end up in the permitted set.

Have you tried adding fI of cap_net_raw to the file to be executed?



> I want to come up with a way to change this that will, convincingly,
> not open up any new security holes. The current concept of process
> inheritable capabilities seems so vague and so oddly defined that I'm
> not sure I want to touch it. In an ideal world, I'd want pI <= pP and
> fP <= fI to be invariants, and I'd like programs without vfs caps set
> to have fI = <everything>. Making this change will surely break
> something, though.
> I'm looking for ideas.
> --Andy
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