[pve-devel] [RFC container 2/3] add feature flags using apparmor profile generation

Wolfgang Bumiller w.bumiller at proxmox.com
Tue Jul 31 14:49:59 CEST 2018


Signed-off-by: Wolfgang Bumiller <w.bumiller at proxmox.com>
---
 debian/control        |   2 +-
 src/PVE/LXC.pm        | 101 +++++++++++++++++++++++++++++++++++++++++++++++++-
 src/PVE/LXC/Config.pm |  53 ++++++++++++++++++++++++++
 3 files changed, 153 insertions(+), 3 deletions(-)

diff --git a/debian/control b/debian/control
index 7fbea8d..b3491c9 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,
 Standards-Version: 3.8.4
diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
index bc03792..46222ba 100644
--- a/src/PVE/LXC.pm
+++ b/src/PVE/LXC.pm
@@ -27,6 +27,8 @@ use PVE::Syscall;
 use PVE::LXC::Config;
 use Time::HiRes qw (gettimeofday);
 
+my $LXC_CONFIG_PATH = '/usr/share/lxc/config';
+
 my $nodename = PVE::INotify::nodename();
 
 my $cpuinfo= PVE::ProcFSTools::read_cpuinfo();
@@ -368,6 +370,94 @@ sub get_cgroup_subsystems {
 	return wantarray ? ($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) = @_;
 
@@ -386,7 +476,7 @@ sub update_lxc_config {
     $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 $ostype = $conf->{ostype} || die "missing 'ostype' - internal error";
 
@@ -398,9 +488,16 @@ sub update_lxc_config {
 	$inc = "$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 || $custom_idmap,
+				$features);
+
+    $raw .= make_apparmor_config($conf, $unprivileged || $custom_idmap,
+				 $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
diff --git a/src/PVE/LXC/Config.pm b/src/PVE/LXC/Config.pm
index a2693d7..9f6765e 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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