Fix auth bypass in authselect pam substacks
Resolves: https://redhat.atlassian.net/browse/RHEL-194086
This commit is contained in:
Joan Torres Lopez
parent
4558239f31
commit
e95c354195
124
0001-data-Add-PAM-substack-wrappers-to-prevent-auth-bypas.patch
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124
0001-data-Add-PAM-substack-wrappers-to-prevent-auth-bypas.patch
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@ -0,0 +1,124 @@
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From 2892ac533be818826b4a1ab3c10a9619632e3a81 Mon Sep 17 00:00:00 2001
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From: Joan Torres Lopez <joantolo@redhat.com>
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Date: Thu, 9 Jul 2026 20:09:10 +0200
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Subject: [PATCH] data: Add PAM substack wrappers to prevent auth bypass on
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empty service files
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When an authselect-managed service file (e.g., switchable-auth) is missing
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or empty, a direct substack to it returns PAM_SUCCESS without checking any
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credentials, allowing unauthenticated session access.
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Introduce generated wrapper PAM services (gdm-*-substack) that use include
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instead of substack internally, followed by pam_deny.so as a safety net.
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The gdm-* services now substack these wrappers: on a properly configured
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system, sufficient modules trigger done before reaching pam_deny.so; on an
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empty or missing service file, pam_deny.so catches the fallthrough.
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---
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data/meson.build | 20 +++++++++++++++++++
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data/pam-redhat/gdm-fingerprint.pam | 2 +-
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data/pam-redhat/gdm-password.pam | 4 ++--
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.../gdm-service-auth-substack.pam.in | 5 +++++
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data/pam-redhat/gdm-smartcard.pam | 2 +-
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data/pam-redhat/gdm-switchable-auth.pam | 4 ++--
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6 files changed, 31 insertions(+), 6 deletions(-)
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create mode 100644 data/pam-redhat/gdm-service-auth-substack.pam.in
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diff --git a/data/meson.build b/data/meson.build
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index 2c5cf94..795f226 100644
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--- a/data/meson.build
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+++ b/data/meson.build
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@@ -134,6 +134,26 @@ pam_data_files_map = {
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],
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}
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+if default_pam_config == 'redhat'
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+ pam_substack_services = [
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+ 'password-auth',
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+ 'smartcard-auth',
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+ 'fingerprint-auth',
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+ 'switchable-auth',
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+ ]
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+ foreach service : pam_substack_services
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+ pam_conf = configuration_data()
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+ pam_conf.set('PAM_SERVICE', service)
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+ configure_file(
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+ input: 'pam-redhat/gdm-service-auth-substack.pam.in',
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+ output: 'gdm-@0@-substack'.format(service),
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+ configuration: pam_conf,
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+ install: true,
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+ install_dir: pam_profiles_dir,
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+ )
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+ endforeach
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+endif
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+
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pam_data_files = pam_data_files_map.get(default_pam_config, [])
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foreach _pam_filename : pam_data_files
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install_data('pam-@0@/@1@.pam'.format(default_pam_config, _pam_filename),
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diff --git a/data/pam-redhat/gdm-fingerprint.pam b/data/pam-redhat/gdm-fingerprint.pam
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index 628568e..b2eddec 100644
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--- a/data/pam-redhat/gdm-fingerprint.pam
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+++ b/data/pam-redhat/gdm-fingerprint.pam
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@@ -1,4 +1,4 @@
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-auth substack fingerprint-auth
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+auth substack gdm-fingerprint-auth-substack
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auth include postlogin
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account required pam_nologin.so
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diff --git a/data/pam-redhat/gdm-password.pam b/data/pam-redhat/gdm-password.pam
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index c75da00..4e331b2 100644
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--- a/data/pam-redhat/gdm-password.pam
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+++ b/data/pam-redhat/gdm-password.pam
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@@ -1,12 +1,12 @@
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auth [success=done ignore=ignore default=bad] pam_selinux_permit.so
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-auth substack password-auth
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+auth substack gdm-password-auth-substack
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auth optional pam_gnome_keyring.so
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auth include postlogin
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account required pam_nologin.so
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account include password-auth
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-password substack password-auth
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+password substack gdm-password-auth-substack
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-password optional pam_gnome_keyring.so use_authtok
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session required pam_selinux.so close
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diff --git a/data/pam-redhat/gdm-service-auth-substack.pam.in b/data/pam-redhat/gdm-service-auth-substack.pam.in
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new file mode 100644
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index 0000000..db43cbb
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--- /dev/null
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+++ b/data/pam-redhat/gdm-service-auth-substack.pam.in
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@@ -0,0 +1,5 @@
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+auth include @PAM_SERVICE@
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+auth required pam_deny.so
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+
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+password include @PAM_SERVICE@
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+password required pam_deny.so
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diff --git a/data/pam-redhat/gdm-smartcard.pam b/data/pam-redhat/gdm-smartcard.pam
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index 3264a71..da1c328 100644
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--- a/data/pam-redhat/gdm-smartcard.pam
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+++ b/data/pam-redhat/gdm-smartcard.pam
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@@ -1,4 +1,4 @@
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-auth substack smartcard-auth
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+auth substack gdm-smartcard-auth-substack
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auth include postlogin
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account required pam_nologin.so
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diff --git a/data/pam-redhat/gdm-switchable-auth.pam b/data/pam-redhat/gdm-switchable-auth.pam
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index 6648c3c..9b7e6de 100644
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--- a/data/pam-redhat/gdm-switchable-auth.pam
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+++ b/data/pam-redhat/gdm-switchable-auth.pam
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@@ -1,11 +1,11 @@
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-auth substack switchable-auth
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+auth substack gdm-switchable-auth-substack
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auth optional pam_gnome_keyring.so
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auth include postlogin
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account required pam_nologin.so
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account include switchable-auth
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-password substack switchable-auth
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+password substack gdm-switchable-auth-substack
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-password optional pam_gnome_keyring.so use_authtok
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session required pam_selinux.so close
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12
gdm.spec
12
gdm.spec
@ -72,6 +72,10 @@ Patch: 0001-session-Don-t-report-service-unavailable-error-as-fa.patch
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# https://gitlab.gnome.org/GNOME/gdm/-/merge_requests/343
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Patch: 0001-local-display-factory-look-for-boot_display-sysfs-at.patch
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# RHEL-194086
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# https://gitlab.gnome.org/GNOME/gdm/-/merge_requests/378
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Patch: 0001-data-Add-PAM-substack-wrappers-to-prevent-auth-bypas.patch
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BuildRequires: dconf
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BuildRequires: desktop-file-utils
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BuildRequires: gettext-devel
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@ -268,7 +272,7 @@ fi
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%config %{_sysconfdir}/gdm/PreSession/*
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%config %{_sysconfdir}/gdm/PostSession/*
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%config %{_sysconfdir}/pam.d/gdm-autologin
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%config %{_sysconfdir}/pam.d/gdm-password
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%config %{_sysconfdir}/pam.d/gdm-password*
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# not config files
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%{_datadir}/gdm/gdm.schemas
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%{_sysconfdir}/dbus-1/system.d/gdm.conf
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@ -311,9 +315,9 @@ fi
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%attr(0700, gdm, gdm) %dir %{_localstatedir}/lib/gdm/.config/pulse
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%attr(0600, gdm, gdm) %{_localstatedir}/lib/gdm/.config/pulse/default.pa
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%attr(0711, root, gdm) %dir /run/gdm
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%config %{_sysconfdir}/pam.d/gdm-smartcard
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%config %{_sysconfdir}/pam.d/gdm-switchable-auth
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%config %{_sysconfdir}/pam.d/gdm-fingerprint
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%config %{_sysconfdir}/pam.d/gdm-smartcard*
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%config %{_sysconfdir}/pam.d/gdm-switchable*
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%config %{_sysconfdir}/pam.d/gdm-fingerprint*
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%{_sysconfdir}/pam.d/gdm-launch-environment
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%{_unitdir}/gdm.service
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%{_unitdir}/gnome-headless-session@.service
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