On Mon, Dec 15, 2025 at 06:41:59PM +0100, Filip Schauer wrote:
> 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 <[email protected]>
> ---
> 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 = $oci_config_get_checked_scalar->('User')) {
This code should be factored into a separate sub.
> + my ($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(/:/, $line);
A subtlety about this sub is that currently the last field also includes
the trailing `\n`. Should probably add a comment, or `chomp` it away,
even if we currently don't use the final field via `$ret_index`.
> + 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/^[^:]*:[^:]*:([^:]*):(?:[^,]*,)*$username(?:,|$)/);
Username comes from the outside and is only limited to not containing a
colon. To use it inside a regex you'd have to quote it as
`\Q$username\E`.
Safer would be to do what you do in `$lookup_field` and just split on
`:` then `,` then grep with `eq`.
> + }
> + 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
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