Hi, Grzegorz Gutowski (gzegzol) wrote on 2014-04-29: "Without suid it seems that call (with correct username) to getspnam in function get_account_info in file passverify.c in pam/modules/pam_unix returns NULL. I don't understand this behaviour. I wrote a simple c program that calls getspnam and it works as expected when called from unprivileged user."
A call to getspnam(3) as an unprivileged user returns NULL; that's expected. (nss_compat returns errno = EACCESS since we can't read /etc/shadow; nss_ldapd returns errno = ENOENT as a generic "not found" code.) The unix_chkpwd helper is sgid to shadow so that it can read /etc/shadow, but nss_ldapd still returns ENOENT to shadow queries. If we make unix_chkpwd suid, then nss_ldapd returns real shadow results; but this is only a workaround (and a potentially dangerous one, at that). What I see happening when I attempt to unlock the screen: - the auth stack is fine; - in the account stack, pam_unix returns PAM_AUTHINFO_UNAVAIL (from unix_chkpwd), and it falls into pam_deny after that (since pam_ldap is Additional). gnome-screensaver works only because it actually ignores the result from the account stack and proceeds anyway: http://bazaar.launchpad.net /~ubuntu-branches/ubuntu/trusty/gnome-screensaver/trusty/view/head:/src /gs-auth-pam.c#L519 Some possible workarounds are: - chmod u+s /sbin/unix_chkpwd (potentially dangerous, not recommended); - dpkg-reconfigure libnss-ldapd and disable the shadow service (then pam_unix doesn't try consulting it); - use libnss-ldap instead of libnss-ldapd, since it allows everyone to read shadow entries; - use libnss-sss instead of libnss-ldapd, since it does not support the shadow service at all (in trusty, at least); - make libpam-ldapd's account rule Primary instead of Additional (but this was already done and subsequently reverted by its maintainer in 0.8.8-1 and 0.8.8-2). I'm not sure why some people reported experiencing this bug when using libnss-ldap or libnss-sss. I'd want to review their PAM and NSS setups in that case. This is all about trusty so far... still have to look at utopic/vivid. -- You received this bug notification because you are a member of DX Packages, which is subscribed to unity in Ubuntu. Matching subscriptions: dx-packages https://bugs.launchpad.net/bugs/1314095 Title: Unity Lockscreen in 14.04 can't unlock when using LDAP account Status in Unity: Confirmed Status in unity package in Ubuntu: Confirmed Bug description: My setup is: Ubuntu 14.04 LTS, ldap accounts, krb5 authentication, Lightdm, Unity session ldap+krb5 is configured using nss-ldapd and nslcd. It works fine. getent passwd and getent shadow works fine. I am able to login in console without any problems. I was able to login in lightdm. Then I used the lock screen. I could not disable the lock screen using my password. I rebooted my computer. Now: After logging in through lightdm, the unity lockscreen locks the screen immediately and I can not disable it using my password. From my short inspection of auth.log and unix_chkpwd sources it seems, that unix_chkpwd works fine when called from lightdm and fails to get user info when called from unity lockscreen. lsb_release -rd Description: Ubuntu 14.04 LTS Release: 14.04 apt-cache policy unity lightdm libpam-modules unity: Installed: 7.2.0+14.04.20140416-0ubuntu1 Candidate: 7.2.0+14.04.20140416-0ubuntu1 Version table: *** 7.2.0+14.04.20140416-0ubuntu1 0 500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages 100 /var/lib/dpkg/status lightdm: Installed: 1.10.0-0ubuntu3 Candidate: 1.10.0-0ubuntu3 Version table: *** 1.10.0-0ubuntu3 0 500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages 100 /var/lib/dpkg/status libpam-modules: Installed: 1.1.8-1ubuntu2 Candidate: 1.1.8-1ubuntu2 Version table: *** 1.1.8-1ubuntu2 0 500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages 100 /var/lib/dpkg/status Contents of /var/log/auth.log: Apr 29 06:49:27 localhost lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "user" Apr 29 06:49:31 localhost lightdm: pam_unix(lightdm:auth): authentication failure; logname= uid=0 euid=0 tty=:2 ruser= rhost= user=user Apr 29 06:49:31 localhost lightdm: pam_krb5(lightdm:auth): user user authenticated as user@NETWORK Apr 29 06:49:32 localhost lightdm[15604]: pam_unix(lightdm-greeter:session): session closed for user lightdm Apr 29 06:49:37 localhost unix_chkpwd[15825]: check pass; user unknown Apr 29 06:49:37 localhost unix_chkpwd[15825]: password check failed for user (user) Apr 29 06:49:37 localhost compiz: pam_unix(lightdm:auth): authentication failure; logname= uid=1001 euid=1001 tty= ruser= rhost= user=user Apr 29 06:49:37 localhost compiz: pam_krb5(lightdm:auth): user user authenticated as user@NETWORK Apr 29 06:49:37 localhost unix_chkpwd[15826]: could not obtain user info (user) Apr 29 06:49:37 localhost unix_chkpwd[15827]: could not obtain user info (user) Apr 29 06:49:37 localhost compiz: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "user" cat /etc/pam.d/common-auth account required pam_unix.so auth required pam_group.so auth [success=2 default=ignore] pam_unix.so try_first_pass nullok_secure auth [success=1 default=ignore] pam_krb5.so try_first_pass minimum_uid=200 auth requisite pam_deny.so auth required pam_permit.so auth optional pam_afs_session.so minimum_uid=200 auth optional pam_ecryptfs.so unwrap auth optional pam_cap.so cat /etc/pam.d/common-account account required pam_unix.so cat /etc/pam.d/lightdm auth requisite pam_nologin.so auth sufficient pam_succeed_if.so user ingroup nopasswdlogin @include common-auth auth optional pam_gnome_keyring.so @include common-account session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so close auth optional pam_group.so session required pam_limits.so @include common-session session [success=ok ignore=ignore module_unknown=ignore default=bad] pam_selinux.so open session optional pam_gnome_keyring.so auto_start session required pam_env.so readenv=1 session required pam_env.so readenv=1 user_readenv=1 envfile=/etc/default/locale @include common-password To manage notifications about this bug go to: https://bugs.launchpad.net/unity/+bug/1314095/+subscriptions -- Mailing list: https://launchpad.net/~dx-packages Post to : dx-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~dx-packages More help : https://help.launchpad.net/ListHelp
