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Re: [libvirt] [PATCH] util: fix clear_emulator_capabilities=0



On 03/13/2013 01:37 PM, Laine Stump wrote:
> My commit 7a2e845a865dc7fa82d2393ea2a770cfc8cf00b4 (and its
> prerequisites) managed to effectively ignore the
> clear_emulator_capabilities setting in qemu.conf (visible in the code
> as the VIR_EXEC_CLEAR_CAPS flag when qemu is being exec'ed), with the
> result that the capabilities are always cleared regardless of the
> qemu.conf setting. This patch fixes it by passing the flag through to
> virSetUIDGIDWithCaps(), which uses it to decide whether or not to
> clear existing capabilities before adding in those that were
> requested.
> 
> Note that the existing capabilities are *always* cleared if the new
> process is going to run as non-root, since the whole point of running
> non-root is to have the capabilities removed (it's still possible to
> add back individual capabilities as needed though).
> ---
> This will need to be backported to v1.0.3-maint.

Yeah, now that Fedora 19 has branched and settled on 1.0.3 as its
starting point, it looks like v1.0.3-maint will be getting lots of fixes :)

> +        if (virSetUIDGIDWithCaps(cmd->uid, cmd->gid, cmd->capabilities,
> +                                 (cmd->flags & VIR_EXEC_CLEAR_CAPS)) < 0) {

While gnulib guarantees that we have <stdbool.h>, it also states that we
cannot rely on C99 rules for slamming random integers into 1 when
converting into a bool context (especially true for C89 compilers using
gnulib's emulation, but apparently there are also buggy C99 compilers
that miscompile things).  This should use '(cmd->flags &
VIR_EXEC_CLEAR_CAPS) != 0' (or !! if you don't like != 0), just to be safe.

> +    /* First drop all caps (unless the requested uid is "unchanged" or
> +     * root and clearExistingCaps wasn't requested), then add back
> +     * those in capBits + the extra ones we need to change uid/gid and
> +     * change the capabilities bounding set.
>       */
>  
> -    capng_clear(CAPNG_SELECT_BOTH);
> +    if (clearExistingCaps || (uid != 1 && uid != 0))

Did you mean uid != 0?

ACK with those problems addressed.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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