[pve-devel] [PATCH v2 container 2/2] add feature flags using apparmor profile generation
Wolfgang Bumiller
w.bumiller at proxmox.com
Tue Oct 2 11:13:38 CEST 2018
Signed-off-by: Wolfgang Bumiller <w.bumiller at proxmox.com>
---
Changes to v1:
* In the start code now $unprivileged now means just that, regardless of
whether the $conf->{unprivileged} option or a custom id map is set.
$custom_idmap is now only used where required.
* Access to 'features' is now limited to root at pam in this patch rather
than a separate patch as it's a much smaller change now (2 lines).
debian/control | 2 +-
src/PVE/LXC.pm | 105 ++++++++++++++++++++++++++++++++++++++++++++++++--
src/PVE/LXC/Config.pm | 53 +++++++++++++++++++++++++
3 files changed, 155 insertions(+), 5 deletions(-)
diff --git a/debian/control b/debian/control
index b688ce0..d1226dd 100644
--- a/debian/control
+++ b/debian/control
@@ -7,7 +7,7 @@ Build-Depends: debhelper (>= 7.0.50~),
libpve-guest-common-perl | libpve-common-perl (<= 4.0-89),
libpve-storage-perl,
libtest-mockmodule-perl,
- lxc (>= 2.1.0-1) | lxc-pve (>= 2.1.0-1),
+ lxc (>= 3.0.2-1) | lxc-pve (>= 3.0.1+pve1-1),
pve-cluster (>= 4.0-8),
pve-doc-generator,
pve-firewall,
diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
index 0b57ae9..89f289e 100644
--- a/src/PVE/LXC.pm
+++ b/src/PVE/LXC.pm
@@ -29,6 +29,8 @@ use PVE::LXC::Config;
use Time::HiRes qw (gettimeofday);
+my $LXC_CONFIG_PATH = '/usr/share/lxc/config';
+
my $nodename = PVE::INotify::nodename();
my $cpuinfo= PVE::ProcFSTools::read_cpuinfo();
@@ -413,6 +415,94 @@ sub get_cgroup_subsystems {
return wantarray ? ($v1, $v2) : $v1;
}
+# Currently we do not need to create seccomp profile 'files' as the only
+# choice our configuration actually allows is "with or without keyctl()",
+# so we distinguish between using lxc's "default" seccomp profile and our
+# added pve-userns.seccomp file.
+#
+# This returns a configuration line added to the raw lxc config.
+sub make_seccomp_config {
+ my ($conf, $unprivileged, $features) = @_;
+ # User-configured profile has precedence, note that the user's entry would
+ # be written 'after' this line anyway...
+ if (PVE::LXC::Config->has_lxc_entry($conf, 'lxc.seccomp.profile')) {
+ # Warn the user if this conflicts with a feature:
+ if ($features->{keyctl}) {
+ warn "explicitly configured lxc.seccomp.profile overrides the following settings: features:keyctl\n";
+ }
+ return '';
+ }
+
+ # Privileged containers keep using the default (which is already part of
+ # the files included via lxc.include, so we don't need to write it out,
+ # that way it stays admin-configurable via /usr/share/lxc/config/... as
+ # well)
+ return '' if !$unprivileged;
+
+ # Unprivileged containers will get keyctl() disabled by default as a
+ # workaround for systemd-networkd behavior. But we have an option to
+ # explicitly enable it:
+ return '' if $features->{keyctl};
+
+ # Finally we're in an unprivileged container without `keyctl` set
+ # explicitly. We have a file prepared for this:
+ return "lxc.seccomp.profile = $LXC_CONFIG_PATH/pve-userns.seccomp\n";
+}
+
+# Since lxc-3.0.2 we can have lxc generate a profile for the container
+# automatically. The default should be equivalent to the old
+# `lxc-container-default-cgns` profile.
+#
+# Additionally this also added `lxc.apparmor.raw` which can be used to inject
+# additional lines into the profile. We can use that to allow mounting specific
+# file systems.
+sub make_apparmor_config {
+ my ($conf, $unprivileged, $features) = @_;
+
+ # user-configured profile has precedence, but first we go through our own
+ # code to figure out whether we should warn the user:
+
+ my $raw = "lxc.apparmor.profile = generated\n";
+ my @profile_uses;
+
+ # There's lxc.apparmor.allow_nesting now, which will add the necessary
+ # apparmor lines, create an apparmor namespace for the container, but also
+ # adds proc and sysfs mounts to /dev/.lxc/{proc,sys}. These do not have
+ # lxcfs mounted over them, because that would prevent the container from
+ # mounting new instances of them for nested containers.
+ if ($features->{nesting}) {
+ push @profile_uses, 'features:nesting';
+ $raw .= "lxc.apparmor.allow_nesting = 1\n"
+ } else {
+ # In the default profile in /etc/apparmor.d we patch this in because
+ # otherwise a container can for example run `chown` on /sys, breaking
+ # access to it for non-CAP_DAC_OVERRIDE tools on the host:
+ $raw .= "lxc.apparmor.raw = deny mount -> /proc/,\n";
+ $raw .= "lxc.apparmor.raw = deny mount -> /sys/,\n";
+ # Preferably we could use the 'remount' flag but this does not sit well
+ # with apparmor_parser currently:
+ # mount options=(rw, nosuid, nodev, noexec, remount) -> /sys/,
+ }
+
+ if (my $mount = $features->{mount}) {
+ push @profile_uses, 'features:mount';
+ foreach my $fs (PVE::Tools::split_list($mount)) {
+ $raw .= "lxc.apparmor.raw = mount fstype=$fs,\n";
+ }
+ }
+
+ # More to come?
+
+ if (PVE::LXC::Config->has_lxc_entry($conf, 'lxc.apparmor.profile')) {
+ if (length(my $used = join(', ', @profile_uses))) {
+ warn "explicitly configured lxc.apparmor.profile overrides the following settings: $used\n";
+ }
+ return '';
+ }
+
+ return $raw;
+}
+
sub update_lxc_config {
my ($vmid, $conf) = @_;
@@ -430,8 +520,8 @@ sub update_lxc_config {
die "missing 'arch' - internal error" if !$conf->{arch};
$raw .= "lxc.arch = $conf->{arch}\n";
- my $unprivileged = $conf->{unprivileged};
- my $custom_idmap = grep { $_->[0] eq 'lxc.idmap' } @{$conf->{lxc}};
+ my $custom_idmap = PVE::LXC::Config->has_lxc_entry($conf, 'lxc.idmap');
+ my $unprivileged = $conf->{unprivileged} || $custom_idmap;
my $ostype = $conf->{ostype} || die "missing 'ostype' - internal error";
@@ -439,13 +529,17 @@ sub update_lxc_config {
my $inc = "$cfgpath/$ostype.common.conf";
$inc ="$cfgpath/common.conf" if !-f $inc;
$raw .= "lxc.include = $inc\n";
- if ($unprivileged || $custom_idmap) {
+ if ($unprivileged) {
$inc = "$cfgpath/$ostype.userns.conf";
$inc = "$cfgpath/userns.conf" if !-f $inc;
$raw .= "lxc.include = $inc\n";
- $raw .= "lxc.seccomp.profile = $cfgpath/pve-userns.seccomp\n";
}
+ my $features = PVE::LXC::Config->parse_features($conf->{features});
+
+ $raw .= make_seccomp_config($conf, $unprivileged, $features);
+ $raw .= make_apparmor_config($conf, $unprivileged, $features);
+
# WARNING: DO NOT REMOVE this without making sure that loop device nodes
# cannot be exposed to the container with r/w access (cgroup perms).
# When this is enabled mounts will still remain in the monitor's namespace
@@ -1001,6 +1095,9 @@ sub check_ct_modify_config_perm {
} elsif ($opt =~ m/^net\d+$/ || $opt eq 'nameserver' ||
$opt eq 'searchdomain' || $opt eq 'hostname') {
$rpcenv->check_vm_perm($authuser, $vmid, $pool, ['VM.Config.Network']);
+ } elsif ($opt eq 'features') {
+ # For now this is restricted to root at pam
+ raise_perm_exc("changing feature flags is only allowed for root\@pam");
} else {
$rpcenv->check_vm_perm($authuser, $vmid, $pool, ['VM.Config.Options']);
}
diff --git a/src/PVE/LXC/Config.pm b/src/PVE/LXC/Config.pm
index c21b69e..cde2445 100644
--- a/src/PVE/LXC/Config.pm
+++ b/src/PVE/LXC/Config.pm
@@ -272,6 +272,41 @@ PVE::JSONSchema::register_standard_option('pve-lxc-snapshot-name', {
maxLength => 40,
});
+my $features_desc = {
+ mount => {
+ optional => 1,
+ type => 'string',
+ description => "Allow mounting file systems of specific types."
+ ." This should be a list of file system types as used with the mount command."
+ ." Note that this can have negative effects on the container's security."
+ ." With access to a loop device, mounting a file can circumvent the mknod"
+ ." permission of the devices cgroup, mounting an NFS file system can"
+ ." block the host's I/O completely and prevent it from rebooting, etc.",
+ format_description => 'fstype;fstype;...',
+ pattern => qr/[a-zA-Z0-9; ]+/,
+ },
+ nesting => {
+ optional => 1,
+ type => 'boolean',
+ default => 0,
+ description => "Allow nesting."
+ ." Best used with unprivileged containers with additional id mapping."
+ ." Note that this will expose procfs and sysfs contents of the host"
+ ." to the guest.",
+ },
+ keyctl => {
+ optional => 1,
+ type => 'boolean',
+ default => 0,
+ description => "For unprivileged containers only: Allow the use of the keyctl() system call."
+ ." This is required to use docker inside a container."
+ ." By default unprivileged containers will see this system call as non-existent."
+ ." This is mostly a workaround for systemd-networkd, as it will treat it as a fatal"
+ ." error when some keyctl() operations are denied by the kernel due to lacking permissions."
+ ." Essentially, you can choose between running systemd-networkd or docker.",
+ },
+};
+
my $confdesc = {
lock => {
optional => 1,
@@ -409,6 +444,12 @@ my $confdesc = {
description => "Makes the container run as unprivileged user. (Should not be modified manually.)",
default => 0,
},
+ features => {
+ optional => 1,
+ type => 'string',
+ format => $features_desc,
+ description => "Allow containers access to advanced features.",
+ },
};
my $valid_lxc_conf_keys = {
@@ -872,6 +913,9 @@ sub update_pct_config {
}
} elsif ($opt eq 'unprivileged') {
die "unable to delete read-only option: '$opt'\n";
+ } elsif ($opt eq 'features') {
+ next if $hotplug_error->($opt);
+ delete $conf->{$opt};
} else {
die "implement me (delete: $opt)"
}
@@ -1025,6 +1069,9 @@ sub update_pct_config {
} elsif ($opt eq 'ostype') {
next if $hotplug_error->($opt);
$conf->{$opt} = $value;
+ } elsif ($opt eq 'features') {
+ next if $hotplug_error->($opt);
+ $conf->{$opt} = $value;
} else {
die "implement me: $opt";
}
@@ -1176,6 +1223,12 @@ sub parse_lxc_network {
return $res;
}
+sub parse_features {
+ my ($class, $data) = @_;
+ return {} if !$data;
+ return PVE::JSONSchema::parse_property_string($features_desc, $data);
+}
+
sub option_exists {
my ($class, $name) = @_;
--
2.11.0
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