[libvirt] [PATCH] m4: Change default QEMU credentials to qemu:qemu

[Daniel P. Berrangé]

On Tue, Mar 26, 2019 at 12:49:28PM +0100, Andrea Bolognani wrote:
> Our current defaults are root:wheel on FreeBSD and macOS, root:root
> everywhere else.
> 
> Looking at what downstream distributions actually do, we can see that
> these defaults are overriden the vast majority of the time, with a
> number of variations showing up in the wild:
> 
>   * qemu:qemu -> Used by CentOS, Fedora, Gentoo, OpenSUSE, RHEL
>                  and... As it turns out, our very own spec file :)
> 
>   * libvirt-qemu:libvirt-qemu -> Used by Debian.
> 
>   * libvirt-qemu:kvm -> Used by Ubuntu.
> 
>   * nobody:nobody -> Used by Arch Linux.
> 
> Based on the above, we can conclude that qemu:qemu are the preferred
> credentials to be used when spawning a QEMU process, while our
> current defaults get very little love.
> 
> Changing our defaults aligns with what most downstreams are actually
> doing, promotes running QEMU under a non-root user - which is a very
> good idea anyway - and shields random people building libvirt from
> source from unwittingly running their guests as root.

While I understand the motivation, this impl is problematic because
it will guarantee that someone building & installing libvirt from
source on Debian, Ubuntu and Arch will have a non-functional QEMU
driver as it will try to use a "qemu:qemu" user/group which does
not exist on those distros.

If we want to change this, we must ensure that we honour the distro
specific user/group names you show above, and fallback to root/root
for distros we don't know about.

> 
> Note that there are a very small number of downstreams that don't
> override our defaults: Alpine Linux, FreeBSD and macOS. Of those,
> only Alpine Linux is affected by this change; all three should
> arguably have been setting --with-qemu-user and --with-qemu-group
> explicitly regardless of this change.
> 
> Signed-off-by: Andrea Bolognani <abologna at redhat.com>
> ---
> 
> Proof that I'm not making any of this up ;)
> 
>   * Alpine Linux
>     https://github.com/alpinelinux/aports/blob/master/main/libvirt/APKBUILD
> 
>   * Arch Linux
>     https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=libvirt-git#n113
> 
>   * CentOS
>     https://git.centos.org/blob/rpms!libvirt.git/8d86411e5109d791edf49c7f43c08a06b80896af/SPECS!libvirt.spec#L226
> 
>   * Debian
>     https://salsa.debian.org/libvirt-team/libvirt/blob/debian/sid/debian/rules#L94-95
> 
>   * Fedora
>     https://src.fedoraproject.org/rpms/libvirt/blob/f29/f/libvirt.spec#_204
> 
>   * FreeBSD
>     https://github.com/freebsd/freebsd-ports/blob/master/devel/libvirt/Makefile
> 
>   * Gentoo
>     https://github.com/gentoo/gentoo/blob/master/app-emulation/libvirt/libvirt-5.1.0.ebuild#L296-L297
> 
>   * macOS (Homebrew)
>     https://github.com/Homebrew/homebrew-core/blob/master/Formula/libvirt.rb
> 
>   * OpenSUSE
>     https://build.opensuse.org/package/view_file/openSUSE:Leap:15.0:Update/libvirt/libvirt.spec?expand=1
> 
>   * Ubuntu
>     https://git.launchpad.net/ubuntu/+source/libvirt/tree/debian/rules?h=ubuntu/disco#n99
> 
>   * Upstream
>     https://libvirt.org/git/?p=libvirt.git;a=blob;f=libvirt.spec.in;h=b7a35a0fb14f3360eb795c4ec9b0e46171d2e4ec;hb=HEAD#l196
> 
>  m4/virt-driver-qemu.m4 | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/m4/virt-driver-qemu.m4 b/m4/virt-driver-qemu.m4
> index cb05c34265..2a1b86e891 100644
> --- a/m4/virt-driver-qemu.m4
> +++ b/m4/virt-driver-qemu.m4
> @@ -44,8 +44,8 @@ AC_DEFUN([LIBVIRT_DRIVER_CHECK_QEMU], [
>      default_qemu_user=root
>      default_qemu_group=wheel
>    else
> -    default_qemu_user=root
> -    default_qemu_group=root
> +    default_qemu_user=qemu
> +    default_qemu_group=qemu

This would need to be much more clever

Regards,
Daniel
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