selinux: Use auth_read_passwd() interface for all our getpwnam() needs

If passt or pasta are started as root, we need to read the passwd file
(be it /etc/passwd or whatever sssd provides) to find out UID and GID
of 'nobody' so that we can switch to it.

Instead of a bunch of allow rules for passwd_file_t and sssd macros,
use the more convenient auth_read_passwd() interface which should
cover our usage of getpwnam().

The existing rules weren't actually enough:

  # strace -e openat passt -f
  [...]
  Started as root, will change to nobody.
  openat(AT_FDCWD, "/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 4
  openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 4
  openat(AT_FDCWD, "/lib64/libnss_sss.so.2", O_RDONLY|O_CLOEXEC) = 4
  openat(AT_FDCWD, "/var/lib/sss/mc/passwd", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
  openat(AT_FDCWD, "/var/lib/sss/mc/passwd", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
  openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 4

with corresponding SELinux warnings logged in audit.log.

Reported-by: Minxi Hou <mhou@redhat.com>
Analysed-by: Miloš Malik <mmalik@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 2 insertions, 12 deletions

diff --git a/contrib/selinux/passt.te b/contrib/selinux/passt.te
index 80bf780..c6cea34 100644
--- a/contrib/selinux/passt.te
+++ b/contrib/selinux/passt.te
@@ -47,8 +47,6 @@ require {
 	type port_t;
 	type http_port_t;
 
-	type passwd_file_t;
-
 	class netlink_route_socket { bind create nlmsg_read };
 	type sysctl_net_t;
 
@@ -96,8 +94,7 @@ allow passt_t self:capability { sys_tty_config setpcap net_bind_service setuid s
 allow passt_t self:cap_userns { setpcap sys_admin sys_ptrace };
 allow passt_t self:user_namespace create;
 
-allow passt_t passwd_file_t:file read_file_perms;
-sssd_search_lib(passt_t)
+auth_read_passwd(passt_t)
 
 allow passt_t proc_net_t:file read;
 allow passt_t net_conf_t:file { open read };
diff --git a/contrib/selinux/pasta.te b/contrib/selinux/pasta.te
index 310383c..69be081 100644
--- a/contrib/selinux/pasta.te
+++ b/contrib/selinux/pasta.te
@@ -68,9 +68,6 @@ require {
 	type system_dbusd_t;
 	type systemd_hostnamed_t;
 	type systemd_systemctl_exec_t;
-	type passwd_file_t;
-	type sssd_public_t;
-	type sssd_var_lib_t;
 	class dbus send_msg;
 	class system module_request;
 	class system status;
@@ -115,8 +112,7 @@ allow pasta_t self:capability { setpcap net_bind_service sys_tty_config dac_read
 allow pasta_t self:cap_userns { setpcap sys_admin sys_ptrace net_admin net_bind_service };
 allow pasta_t self:user_namespace create;
 
-allow pasta_t passwd_file_t:file read_file_perms;
-sssd_search_lib(pasta_t)
+auth_read_passwd(pasta_t)
 
 domain_auto_trans(pasta_t, bin_t, unconfined_t);
 domain_auto_trans(pasta_t, shell_exec_t, unconfined_t);
@@ -178,12 +174,9 @@ allow pasta_t init_t:system status;
 allow pasta_t unconfined_t:dir search;
 allow pasta_t unconfined_t:file read;
 allow pasta_t unconfined_t:lnk_file read;
-allow pasta_t passwd_file_t:file { getattr open read };
 allow pasta_t self:process { setpgid setcap };
 allow pasta_t shell_exec_t:file { execute execute_no_trans map };
 
-allow pasta_t sssd_var_lib_t:dir search;
-allow pasta_t sssd_public_t:dir search;
 allow pasta_t hostname_exec_t:file { execute execute_no_trans getattr open read map };
 allow pasta_t system_dbusd_t:unix_stream_socket connectto;
 allow pasta_t system_dbusd_t:dbus send_msg;