Re: [PATCH] capabilities: Ambient capability set V1

On Thu, Feb 26, 2015 at 12:55 PM, Serge E. Hallyn [off-list ref] wrote:

On Thu, Feb 26, 2015 at 12:51:57PM -0800, Andy Lutomirski wrote:

quoted

On Thu, Feb 26, 2015 at 12:34 PM, Serge E. Hallyn [off-list ref] wrote:

quoted

On Thu, Feb 26, 2015 at 02:13:00PM -0600, Christoph Lameter wrote:

quoted

On Thu, 26 Feb 2015, Serge E. Hallyn wrote:

quoted

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.

Hm, the problem is that then the empty pA is inherited by children.
I do see that any program with fP set should probably run with only
what it requested.  Would

         if (pA && is_empty(fP))
                 pE' = pP'
         else
                 pE' = pP' & fE

help?  Or are you worried about a program with fP set which then
executes other programs?

The particular worry I expressed there was just about pE.

I'm still extremely nervous about allowing nonempty pA to propagate to
setuid or nonzero fP programs.  It's less obviously dangerous if pA is
never a superset of pP, but it could still cause problems with setuid
programs that execute intentionally deprivileged helpers.

--Andy