Quoting Michael Tokarev ([email protected]):
> Hopefully not a flamewar question...
nothing wrong with asking for clarification. Though you should have
copied [email protected].
> Currently, capabilities of a process are reset during exec()
> system call. At least effective+permitted set.
>
> 1) In case new uid != 0, all the caps are cleared, so it is not
> possible to execute a program as non-root but still give it some
> capabilities (like, say, CAP_NET_BIND_SERVICE).
With the introduction of file capabilities in -mm, you can assign
CAP_NET_BIND_SERVICE to a program not owned by root such that all users
can run the program with that capabilities.
Even in mainline, you can make the program setuid 0 and code it such
that it immediately specify keepcaps, change to nonroot, and drop all
caps but CAP_NET_BIND_SERVICE.
> 2) In case new uid == 0, effective and permitted sets are restored
> to all-ones.
>
> This is regardless of other settings, like prctl(KEEPCAPS), or
> the current set of capabilities.
Look at the prctl(2) manpage - it is about keeping capabilities across
setuid, not across exec.
> I partly understand why 2) is done - in case of setuid binary being
> executed, all the capabilities are set for it. But this breaks
> executing non-setuid binaries too -- for example, it'd be very nice
> to be able to chroot to some directory, and remove CAP_SYS_CHROOT
> (and other evil caps like CAP_SYS_MODULE, CAP_SETPCAP) -- this way,
> with minimal efforts, chroot will work almost (yes, I understand
> it's not entirely the same) the same as BSD jail(2) concept.
Are you aware of the namespace/containers work going on right now to get
full virtual server support into mainline? See
http://lists.linux-foundation.org/pipermail/containers/
for the archives of the main relevant mailing list.
> So the question is: why capability sets are being reinitialized during
> exec()? At least in 2.4 era, they weren't... and stuff like
> execcap, sucaps etc was working. Now they aren't anymore.
Please see the file capabilities support in -mm and let us know whether
that does (not) meet your needs.
thanks,
-serge
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