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Date: Mon, 24 Mar 2025 13:38:42 +0100
From: Wolfgang Bumiller <w.bumiller@proxmox.com>
To: Fiona Ebner <f.ebner@proxmox.com>
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Subject: Re: [pve-devel] [PATCH container v5 24/32] add LXC::Namespaces
module
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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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