Re: [pve-devel] [PATCH container v5 24/32] add LXC::Namespaces module

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Fri, Mar 21, 2025 at 02:48:44PM +0100, Fiona Ebner wrote:
> The module includes a run_in_userns() helper to run a Perl subroutine
> in a user namespace.
> 
> The first use case is running the container backup subroutine for
> external providers inside a user namespace. That allows them to see
> the filesystem to back-up from the containers perspective and also
> improves security because of isolation.
> 
> Heavily adapted from code by Wolfgang from the pve-buildpkg
> repository.
> 
> Originally-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
> [FE: add $idmap parameter, drop $aux_groups parameter
>      use different fork helper
>      use newuidmap and newgidmap binaries]
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>  src/PVE/LXC/Makefile      |  1 +
>  src/PVE/LXC/Namespaces.pm | 60 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 61 insertions(+)
>  create mode 100644 src/PVE/LXC/Namespaces.pm
> 
> diff --git a/src/PVE/LXC/Makefile b/src/PVE/LXC/Makefile
> index a190260..4b05e98 100644
> --- a/src/PVE/LXC/Makefile
> +++ b/src/PVE/LXC/Makefile
> @@ -5,6 +5,7 @@ SOURCES= \
>  	Create.pm \
>  	Migrate.pm \
>  	Monitor.pm \
> +	Namespaces.pm \
>  	Setup.pm \
>  	Tools.pm
>  
> diff --git a/src/PVE/LXC/Namespaces.pm b/src/PVE/LXC/Namespaces.pm
> new file mode 100644
> index 0000000..e4b1e5f
> --- /dev/null
> +++ b/src/PVE/LXC/Namespaces.pm
> @@ -0,0 +1,60 @@
> +package PVE::LXC::Namespaces;
> +
> +use strict;
> +use warnings;
> +
> +use Fcntl qw(O_WRONLY);
> +use Socket;
> +
> +use PVE::Tools;
> +
> +use constant {CLONE_NEWNS   => 0x00020000,
> +              CLONE_NEWUSER => 0x10000000};

nit: ^ those can be imported from `PVE::Tools`.

> +
> +my sub set_id_map($$) {
> +    my ($pid, $id_map) = @_;
> +
> +    my @gid_args = ();
> +    my @uid_args = ();
> +
> +    for my $map ($id_map->@*) {
> +	my ($type, $ct, $host, $length) = $map->@*;
> +
> +	push @gid_args, $ct, $host, $length if $type eq 'g';
> +	push @uid_args, $ct, $host, $length if $type eq 'u';
> +    }
> +
> +    PVE::Tools::run_command(['newgidmap', $pid, @gid_args]) if scalar(@gid_args);
> +    PVE::Tools::run_command(['newuidmap', $pid, @uid_args]) if scalar(@uid_args);
> +}
> +
> +sub run_in_userns(&;$) {
> +    my ($code, $id_map) = @_;
> +    socketpair(my $sp, my $sc, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
> +	or die "socketpair: $!\n";
> +    my $child = sub {
> +	close($sp);
> +	PVE::Tools::unshare(CLONE_NEWUSER|CLONE_NEWNS) or die "unshare(NEWUSER|NEWNS): $!\n";
> +	syswrite($sc, "1\n") == 2 or die "write: $!\n";
> +	shutdown($sc, 1);
> +	my $two = <$sc>;
> +	die "failed to sync with parent process\n" if $two ne "2\n";
> +	close($sc);
> +	$! = undef;
> +	($(, $)) = (0, 0); die "$!\n" if $!;
> +	($<, $>) = (0, 0); die "$!\n" if $!;
> +	return $code->();
> +    };
> +    my $parent = sub {
> +	my ($pid) = @_;
> +	close($sc);
> +	my $one = <$sp>;
> +	die "failed to sync with userprocess\n" if $one ne "1\n";
> +	set_id_map($pid, $id_map);
> +	syswrite($sp, "2\n") == 2 or die "write: $!\n";
> +	close($sp);
> +    };
> +    PVE::Tools::run_fork($child, { afterfork => $parent });
> +}
> +
> +1;
> -- 
> 2.39.5


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