Re: Frustrated with capabilities..

Pavel Machek
2008-08-28T14:18:48Z

On Wed 2008-08-27 12:31:10, Markku Savela wrote:
> I just want to run an exectable with limited capabilities and assumed
> the following approach would work fine:
>
> 1) fork process
> 2) in child
>
> 2.1 set current capabilities (eip) using cap_set_proc
> 2.2 execve the executable.
>
> But it frigging does not work! Just before the execve, the result of
> cap_to_text is
>
> = cap_net_bind_service+eip
>
> but, in the execve executable, the result is suddenly
>
> = cap_net_bind_service+i
>
> Why does the execve clear the effective and permitted capabities,
> against my clear instructions? (I also have the prctl KEEP_CAPS set,
> though in this case it should be irrelevant).
>
> - The kernel is from ubuntu distro, 2.6.24.
>
> - the executable *does* *not* have any setuid/setgid bits
>
> - the upcoming file capabities will not be any help, because I will
> need to start the same executable with different capabilities
> depending on context.

Yes, you need upcoming filesystem capabilities. Binary may not
inherit capabilities unless filesystem flags permit that.

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