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feat: osh.pl: jit mfa for plugins

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Stéphane Lesimple 2023-11-02 15:26:12 +00:00 committed by Stéphane Lesimple
parent 926a177aa0
commit b48463076f
5 changed files with 190 additions and 4 deletions
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18
bin/admin/install
View file

@ -52,6 +52,7 @@ set_default_options()
opt[regen-hostkeys]=0
opt[logrotate]=1
opt[overwrite-logrotate]=1
opt[generate-mfa-secret]=1
# special case:
# If $autodetect_startup_system is 1, we'll autodetect whether we will install the
@ -132,7 +133,7 @@ while [ -n "$1" ]; do
modify-pam-lastlog remove-weak-moduli regen-hostkeys overwrite-logrotate overwrite-cron \
overwrite-syslog-ng logrotate cron syslog-ng migration-grant-aclkeeper-to-gatekeepers \
init systemd-units profile modify-pam-sshd wait check-ttyrec install-fake-ttyrec \
install-selinux-module
install-selinux-module generate-mfa-secret
do
if [ "$1" = "--no-$allowedopt" ]; then
opt[$allowedopt]=0
@ -214,6 +215,7 @@ Usage:
--[no-]profile apply our hardened configuration in system profile.d/ [N]
--[no-]remove-weak-moduli remove weak (<4096) moduli from the ssh server moduli file [N]
--[no-]regen-hostkeys generate new host keys (and trash the old ones) for ssh server [N]
--[no-]generate-mfa-secret generate a new MFA token secret, will never overwrite a preexisting one [N, U]
--[no-]logrotate put our logrotate config files in system logrotate.d/ [N, U, M]
--[no-]overwrite-logrotate overwrite possibly existing files in system logrotate.d/ with our templates [N, U]
@ -1265,6 +1267,20 @@ if [ "${opt[remove-weak-moduli]}" = 1 ]; then
fi
fi
if [ "${opt[generate-mfa-secret]}" = 1 ]; then
action_doing "Generate the MFA HMAC secret if needed"
if [ -e "$BASTION_ETC_DIR/mfa-token.conf" ]; then
action_na
else
secret=$(tr -dc A-Za-z0-9 < /dev/urandom | head -c32)
touch "$BASTION_ETC_DIR/mfa-token.conf"
chown 0:bastion-users "$BASTION_ETC_DIR/mfa-token.conf"
chmod 640 "$BASTION_ETC_DIR/mfa-token.conf"
echo '{ "secret": "'"$secret"'" }' > "$BASTION_ETC_DIR/mfa-token.conf"
action_done
fi
fi
# lastly, check for ttyrec version and yell if it's not the proper one
if [ "${opt[check-ttyrec]}" = 1 ] ; then
action_doing "Checking ttyrec version"

166
bin/shell/osh.pl
View file

@ -376,6 +376,8 @@ my $remainingOptions;
"kbd-interactive" => \my $userKbdInteractive,
"proactive-mfa" => \my $proactiveMfa,
"fallback-password-delay=i" => \my $fallbackPasswordDelay,
"generate-mfa-token" => \my $generateMfaToken,
"mfa-token=s" => \my $mfaToken,
);
if (not defined $realOptions) {
help();
@ -463,6 +465,11 @@ if ($bind) {
}
}
if ($generateMfaToken && $mfaToken) {
main_exit OVH::Bastion::EXIT_CONFLICTING_OPTIONS, "conflicting_options",
"Can't specify both --generate-mfa-token and --mfa-token";
}
# if proactive MFA has been requested, do it here, before the code diverts to either
# handling interactive session, plugins/osh commands, or a connection request
if ($proactiveMfa) {
@ -960,7 +967,6 @@ if ($osh_command) {
}
# check if we need JIT MFA to call this plugin, this can be configured per-plugin
# TODO: autodetect if the MFA check is done outside of the code by sshd+PAM, to avoid re-asking for it here
my $MFArequiredForPlugin = OVH::Bastion::plugin_config(plugin => $osh_command, key => "mfa_required")->value;
$MFArequiredForPlugin ||= 'none'; # no config means none
@ -993,6 +999,16 @@ if ($osh_command) {
$bastion_details{'mfa'} = $fnret->value->{'mfaInfo'};
}
# now, check whether this plugin wants us to trigger a JIT MFA check depending on the
# specified user/host/ip, if this is configured in one of the matching bastion groups
# we are a part of (plugins such as sftp or scp will require us to do this, as they can't
# do it themselves, and as they're accessing a remote asset, JIT MFA should apply to them too)
my $pluginJitMfa = OVH::Bastion::plugin_config(plugin => $osh_command, key => "jit_mfa")->value;
if ($pluginJitMfa) {
$fnret = do_plugin_jit_mfa(pluginJitMfa => $pluginJitMfa);
# do_plugin_jit_mfa exits if needed, but just in case...
main_exit(OVH::Bastion::EXIT_MFA_FAILED, "jit_mfa_failed", $fnret->msg) if !$fnret;
}
OVH::Bastion::set_terminal_mode_for_plugin(plugin => $osh_command, action => 'set');
# get the execution mode required by the plugin
@ -1724,6 +1740,154 @@ sub do_jit_mfa {
return R('OK');
}
sub do_plugin_jit_mfa {
my %params = @_;
my $pluginJitMfa = $params{'pluginJitMfa'};
my $localfnret;
if (!$host) {
# if no host is specified, and the plugin has jit_mfa_allow_no_host, then
# allow the plugin to be called, for example to show its builtin help()
$localfnret = OVH::Bastion::plugin_config(plugin => $osh_command, key => 'jit_mfa_allow_no_host');
if ($localfnret && $localfnret->value) {
if ($generateMfaToken) {
# return a dummy token so that our caller is happy, then exit
print "MFA_TOKEN=notrequired\n";
main_exit(OVH::Bastion::EXIT_OK);
}
# tell our caller that the plugin can be executed without host
return R('OK_JIT_MFA_NOT_REQUIRED');
}
# otherwise, we need a host
main_exit(OVH::Bastion::EXIT_NO_HOST, 'no_host', "A host is required for this plugin but none was specified");
}
# if no user yet, fix it to remote user
# we need it to be able to get the proper answer for is_access_granted, and we need to
# call is_access_granted so that we know whether we need to trigger JIT MFA for this
# plugin, based on the groups we find
my $remoteuser = $user || $config->{'defaultLogin'} || $remoteself || $sysself;
$localfnret = OVH::Bastion::is_access_granted(
account => $self,
user => $user,
ipfrom => $ipfrom,
ip => $ip,
port => $port,
details => 1
);
if (!$localfnret) {
# not allowed, exit
my $message = $localfnret->msg;
if ($remoteuser eq $self) {
$message .= " (tried with remote user '$remoteuser')";
}
main_exit(OVH::Bastion::EXIT_ACCESS_DENIED, 'access_denied', $message);
}
# else, get the access list
my @accessListForPlugin = @{$localfnret->value || []};
# and check whether we need JIT MFA
my $mfaRequired;
$localfnret = get_details_from_access_array(
accessList => \@accessListForPlugin,
quiet => ($quiet || $mfaToken),
useKey => $useKey
);
if ($localfnret && $localfnret->value->{'mfaRequired'}) {
$mfaRequired = $localfnret->value->{'mfaRequired'};
}
elsif (!$localfnret) {
main_exit(OVH::Bastion::EXIT_ACCESS_DENIED, "access_denied", $localfnret->msg);
}
# not required? we're done
if (!$mfaRequired) {
if ($generateMfaToken) {
# return a dummy token so that our caller is happy, then exit
print "MFA_TOKEN=notrequired\n";
main_exit(OVH::Bastion::EXIT_OK);
}
# no mfa required and our caller didn't request a token generation, just carry on
return R('OK_JIT_MFA_NOT_REQUIRED');
}
$localfnret = OVH::Bastion::load_configuration_file(
file => OVH::Bastion::main_configuration_directory() . '/mfa-token.conf',
rootonly => 1
);
if (!$localfnret || !$localfnret->value) {
main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed_no_secret',
"No MFA token HMAC secret has been configured, please report to your sysadmin");
}
my $tokenConfig = $localfnret->value;
if (ref $tokenConfig ne 'HASH' || !$tokenConfig->{'secret'} || length($tokenConfig->{'secret'}) < 32) {
main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed_invalid_secret',
"An invalid MFA token HMAC secret has been configured, please report to your sysadmin");
}
my $secret = $tokenConfig->{'secret'};
# so, if JIT MFA is required, we need to have either --generate-mfa-token, or --mfa-token
if ($mfaToken) {
# use stderr here because we might be called by scp or sftp and they don't expect anything on stdout
$ENV{'FORCE_STDERR'} = 1;
# recompute the theoretical token value we should have
my ($then) = $mfaToken =~ m{^v1,(\d+),[a-f0-9]{64}$};
if (!$then) {
main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed_invalid_format',
"Provided MFA token has invalid format");
}
# is the token expired?
if ($then + 15 < time()) {
main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed_expired_token', "Provided MFA token is expired");
}
# is the token in the future?
if ($then > time()) {
main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed_future_token',
"Provided MFA token has creation date in the future");
}
require Digest::SHA;
my $payload = join(',', $then, $self, $host, $port, $remoteuser);
my $theoreticalToken = sprintf("v1,%s,%s", $then, Digest::SHA::hmac_sha256_hex($payload, $secret));
# are both tokens identical?
if ($mfaToken ne $theoreticalToken) {
main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed_invalid_token', "Provided MFA token is invalid");
}
print STDERR "... MFA token is valid, proceeding\n";
return R('OK_JIT_MFA_VALIDATED');
}
elsif ($generateMfaToken) {
print "MFA token generation requested, entering MFA phase...\n";
$localfnret = OVH::Bastion::do_pamtester(self => $self, sysself => $sysself);
$localfnret or main_exit(OVH::Bastion::EXIT_MFA_FAILED, 'mfa_failed', $localfnret->msg);
# if we're still here, MFA has been validated, generate a token, save and return it
require Digest::SHA;
my $now = time();
my $payload = join(',', $now, $self, $host, $port, $remoteuser);
my $generated_token = sprintf("v1,%s,%s", $now, Digest::SHA::hmac_sha256_hex($payload, $secret));
# return token to caller
print "MFA_TOKEN=$generated_token\n";
main_exit(OVH::Bastion::EXIT_OK, "mfa_token_generated", "MFA token has been generated");
}
# MFA required but none provided or requested: bail out
main_exit(OVH::Bastion::EXIT_MFA_FAILED, "jit_mfa_required_no_token",
"JIT MFA is required, but you didn't specify either --generate-mfa-token or --mfa-token");
return; # make perlcritic happy
}
#
# Display help message
#

2
etc/bastion/osh-sync-watcher.rsyncfilter.dist
View file

@ -17,6 +17,8 @@
+ /etc/gshadow
+ /etc/sudoers.d/
+ /etc/sudoers.d/osh-*
+ /etc/bastion/
+ /etc/bastion/mfa-token.conf
+ /etc/ssh/
+ /etc/ssh/ssh_host_*_key
+ /etc/ssh/ssh_host_*_key.pub

6
lib/perl/OVH/Bastion/configuration.inc
View file

@ -21,7 +21,7 @@ sub load_configuration_file {
if ($secure || $rootonly) {
my @stat = lstat($file);
if (@stat) {
if ($stat[4] != 0 or $stat[5] != 0) {
if ($stat[4] != 0) {
return R('ERR_SECURITY_VIOLATION',
msg => "Configuration file ($file) is not owned by root, report to your sysadmin.");
}
@ -29,6 +29,10 @@ sub load_configuration_file {
return R('ERR_SECURITY_VIOLATION',
msg => "Configuration file ($file) is not a regular file, report to your sysadmin.");
}
if (S_IMODE($stat[2]) & S_IWGRP) {
return R('ERR_SECURITY_VIOLATION',
msg => "Configuration file ($file) is group-writable, report to your sysadmin.");
}
if (S_IMODE($stat[2]) & S_IWOTH) {
return R('ERR_SECURITY_VIOLATION',
msg => "Configuration file ($file) is world-writable, report to your sysadmin.");

2
tests/functional/launch_tests_on_instance.sh
View file

@ -708,7 +708,7 @@ runtests()
# craft a test that always work and will notice that the previous one failed, which'll display
# the verbose error information
modulename=main
success done true
success "done" true
}
COUNTONLY=0