[libvirt] Fwd: libvirtd failing on MacOS in setgroups

[Daniel P. Berrangé]

On Wed, Aug 21, 2019 at 12:47:03PM -0400, Marcus Furlong wrote:
> On Wed, 21 Aug 2019 at 08:23, Daniel P. Berrangé <berrange at redhat.com> wrote:
> >
> > On Tue, Aug 20, 2019 at 11:11:07AM -0400, Marcus Furlong wrote:
> > > Resend to libvir-list in case that is more appropriate:
> > >
> > >
> > > Hi,
> > >
> > > I get the following error when running libvirtd on MacOS as root:
> > >
> > > 2019-07-11 00:12:33.673+0000: 123145573953536: error :
> > > qemuProcessQMPLaunch:8501 : internal error: Failed to start QEMU
> > > binary /usr/local/bin/qemu-system-x86_64 for probing: libvirt:  error
> > > : cannot set supplemental groups: Invalid argument
> >
> > Are you able to run 'strace' (or whatever MacOS eqiuv is) to see
> > the values passed to setgroups when it fails ?
> 
> I ran `dtruss -f -l -s /usr/local/sbin/libvirtd` but the setgroups
> calls seem to be missing.
> 
> Looking at other sources, it seems like some have special treatment of
> setgroups on MacOS, e.g. samba:
> 
>    https://github.com/samba-team/samba/blob/v4-11-stable/source3/smbd/sec_ctx.c#L261-#L305
> 
> Perhaps this is needed for libvirt?

The capping of ngroups to NGROUPS_MAX looks like a possibe reason.

Adding this debug might show us if we're exceeding it:

diff --git a/src/util/virutil.c b/src/util/virutil.c
index 89d2cf011f..effc02b898 100644
--- a/src/util/virutil.c
+++ b/src/util/virutil.c
@@ -1043,6 +1043,7 @@ virSetUIDGID(uid_t uid, gid_t gid, gid_t *groups ATTRIBUTE_UNUSED,
     }
 
 # if HAVE_SETGROUPS
+    VIR_DEBUG("setgroups %d max %d", ngroups, NGROUPS_MAX);
     if (gid != (gid_t)-1 && setgroups(ngroups, groups) < 0) {
         virReportSystemError(errno, "%s",
                              _("cannot set supplemental groups"));


Regards,
Daniel
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