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From: Fiona Ebner <f.ebner@proxmox.com>
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Date: Fri, 21 Mar 2025 14:48:44 +0100
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Subject: [pve-devel] [PATCH container v5 24/32] add LXC::Namespaces module
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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};
+
+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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