[pve-devel] [PATCH container 2/2] oci create: honor `User` from OCI image config

[Filip Schauer]

Honor a custom user and group specified for the entrypoint via the OCI
image config `User` field instead of ignoring it.

User and group name lookups, including supplementary groups, are
resolved from /etc/passwd and /etc/group in the container file system.
This behaviour matches the OCI image spec. [0]

[0] https://specs.opencontainers.org/image-spec/config/?v=v1.1.1#properties

Signed-off-by: Filip Schauer <f.schauer at proxmox.com>
---
This requires the following patch for LXC in order to work properly:
https://github.com/lxc/lxc/pull/4626

 src/PVE/LXC/Create.pm | 59 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/src/PVE/LXC/Create.pm b/src/PVE/LXC/Create.pm
index 9956cf9..08e0386 100644
--- a/src/PVE/LXC/Create.pm
+++ b/src/PVE/LXC/Create.pm
@@ -768,6 +768,65 @@ sub restore_oci_archive {
         }
     }
 
+    if (my $usercfg = $oci_config_get_checked_scalar->('User')) {
+        my ($user, $group) = $usercfg =~ /^([^:]+)(?::([^:]+))?$/
+            or die "OCI config value for 'User' has an invalid format\n";
+
+        my $etc_passwd = "$rootdir/etc/passwd";
+        my $etc_group = "$rootdir/etc/group";
+
+        # Scan file, match column $match_index against $match_val, return value at $ret_index
+        my $lookup_field = sub {
+            my ($file, $match_index, $match_val, $ret_index) = @_;
+
+            open(my $fh, '<', $file) or return undef;
+            while (my $line = <$fh>) {
+                my @fields = split(/:/, $line);
+                if (defined($fields[$match_index]) && $fields[$match_index] eq $match_val) {
+                    return $fields[$ret_index];
+                }
+            }
+            return undef;
+        };
+
+        my $get_supplementary_groups = sub {
+            my ($username) = @_;
+
+            my @groups;
+            open(my $fh, '<', $etc_group) or return undef;
+            while (defined(my $line = <$fh>)) {
+                push @groups, $1
+                    if ($line =~ m/^[^:]*:[^:]*:([^:]*):(?:[^,]*,)*$username(?:,|$)/);
+            }
+            return join(',', @groups);
+        };
+
+        my ($uid, $username, $gid, $groups);
+
+        if ($user =~ /^\d+$/) {
+            $uid = $user;
+            $username = $lookup_field->($etc_passwd, 2, $uid, 0);
+        } else {
+            $username = $user;
+            $uid = $lookup_field->($etc_passwd, 0, $username, 2);
+        }
+
+        if (defined($group)) {
+            if ($group =~ /^\d+$/) {
+                $gid = $group;
+            } else {
+                $gid = $lookup_field->($etc_group, 0, $group, 2);
+            }
+        } else {
+            $gid = $lookup_field->($etc_passwd, 2, $uid, 3) if defined($uid);
+            $groups = $get_supplementary_groups->($username) if defined($username);
+        }
+
+        push $conf->{lxc}->@*, ['lxc.init.uid', $uid] if defined($uid);
+        push $conf->{lxc}->@*, ['lxc.init.gid', $gid] if defined($gid);
+        push $conf->{lxc}->@*, ['lxc.init.groups', $groups] if defined($groups);
+    }
+
     if (my $working_dir = $oci_config_get_checked_scalar->('WorkingDir')) {
         push $conf->{lxc}->@*, ['lxc.init.cwd', $working_dir];
     }
-- 
2.47.3