Re: [PATCH] capabilities: Ambient capability set V1

[Andy Lutomirski]

On Thu, Feb 26, 2015 at 12:34 PM, Serge E. Hallyn <serge@xxxxxxxxxx> wrote:
> On Thu, Feb 26, 2015 at 02:13:00PM -0600, Christoph Lameter wrote:
>> On Thu, 26 Feb 2015, Serge E. Hallyn wrote:
>>
>> > Andrew Morgan was against that.  What if we changed
>> >
>> > pE' = pP' & (fE | pA)
>> >
>> > to
>> >
>> >     if (pA)
>> >             pE' = pP' & fE
>> >     else
>> >             pE' = pP'
>> >
>>
>> Same problem as before. The ambient bits will not be set in pE'.
>
> And what if I weren't scatterbrained and we did
>
>         if (pA)
>                 pE' = pP'
>         else
>                 pE' = pP' & fE
>
> All pP' bits would be set in pE'.

That seems reasonable to me, except for my paranoia:

What if there's a program with CAP_DAC_OVERRIDE in fP and fE set to
the empty set (i.e. the magic effective bit cleared), and the program
relies on that.  A malicious user has CAP_NET_BIND and sets pA =
CAP_NET_BIND.  Boom!

If we changed that to if (pA') and zeroed pA if fP is non-empty then
this problem goes away.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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