linux-kernel - Re: Linux capabilities shouldn't be lost during setuid to non-root from root or to another non-root uid from a non-root uid.

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Date:	Mon, 18 Apr 2011 10:20:43 +0900
From:	crocket <crockabiscuit@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: Linux capabilities shouldn't be lost during setuid to non-root
 from root or to another non-root uid from a non-root uid.

prctl(PR_SET_KEEPCAPS, 1) didn't work since, during setuid to
non-root, effective bit was lost.

Please refer to "man prctl".

I don't know what would happen when I run OpenVPN as non-root with
cap_setuid, cap_setgid, cap_sys_admin.
I guess OpenVPN woull fail to generate tun0 interface if it's run as root.
However, I need to test it to be sure.

On Mon, Apr 18, 2011 at 3:07 AM, Serge E. Hallyn <serge@...lyn.com> wrote:
> You need
>
>        prctl(PR_SET_KEEPCAPS, 1);
>
> man prctl for details.  In particular, see the following example:
>
> #include <stdio.h>
> #include <sys/prctl.h>
> #include <sys/capability.h>
>
> int main()
> {
>        cap_t c;
>        c = cap_get_proc();
>        printf("uid %d, current caps: %s\n", getuid(), cap_to_text(c, NULL));
>        cap_free(c);
>        prctl(PR_SET_KEEPCAPS, 1);
>        setuid(1001, 1001, 1001);
>        c = cap_get_proc();
>        printf("uid %d, current caps: %s\n", getuid(), cap_to_text(c, NULL));
>        cap_free(c);
> }
>
> You can either run that as root, or you can do
>
>        sudo setcap cap_setuid,cap_setgid,cap_sys_admin=eip captest
>
> and then run it as non-root.
>
> HTH,
> -serge
>
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