migrate to new SELinux api

Using hard-coded access vector ids is deprecated and can lead to issues with custom SELinux policies.
Switch to `selinux_check_access()`.

Also use the libselinux log callback and log if available to audit.
This makes it easier for users to catch SELinux denials.

Drop legacy shortcut logic for passwd, which avoided a SELinux check if uid 0 changes a password of a user which username equals the current SELinux user identifier.
Nowadays usernames rarely match SELinux user identifiers and the benefit of skipping a SELinux check is negligible.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>

lib/prototypes.h

@@ -336,6 +336,7 @@ extern /*@observer@*/const char *crypt_make_salt (/*@null@*//*@observer@*/const
 #ifdef WITH_SELINUX
 extern int set_selinux_file_context (const char *dst_name);
 extern int reset_selinux_file_context (void);
+extern int check_selinux_permit (const char *perm_name);
 #endif
 
 /* semanage.c */

lib/selinux.c

@@ -34,6 +34,7 @@
 #include "defines.h"
 
 #include <selinux/selinux.h>
+#include <selinux/context.h>
 #include "prototypes.h"
 
 
@@ -98,6 +99,105 @@ int reset_selinux_file_context (void)
 	return 0;
 }
 
+/*
+ *  Log callback for libselinux internal error reporting.
+ */
+__attribute__((__format__ (printf, 2, 3)))
+static int selinux_log_cb (int type, const char *fmt, ...) {
+	va_list ap;
+	char *buf;
+	int r;
+#ifdef WITH_AUDIT
+	static int selinux_audit_fd = -2;
+#endif
+
+	va_start (ap, fmt);
+	r = vasprintf (&buf, fmt, ap);
+	va_end (ap);
+
+	if (r < 0) {
+		return 0;
+	}
+
+#ifdef WITH_AUDIT
+	if (-2 == selinux_audit_fd) {
+		selinux_audit_fd = audit_open ();
+
+		if (-1 == selinux_audit_fd) {
+			/* You get these only when the kernel doesn't have
+			 * audit compiled in. */
+			if (   (errno != EINVAL)
+			    && (errno != EPROTONOSUPPORT)
+			    && (errno != EAFNOSUPPORT)) {
+
+			    (void) fputs (_("Cannot open audit interface.\n"),
+			              stderr);
+			    SYSLOG ((LOG_WARN, "Cannot open audit interface."));
+			}
+		}
+	}
+
+	if (-1 != selinux_audit_fd) {
+		if (SELINUX_AVC == type) {
+			if (audit_log_user_avc_message (selinux_audit_fd,
+			    AUDIT_USER_AVC, buf, NULL, NULL,
+			    NULL, 0) > 0) {
+				goto skip_syslog;
+			}
+		} else if (SELINUX_ERROR == type) {
+			if (audit_log_user_avc_message (selinux_audit_fd,
+			    AUDIT_USER_SELINUX_ERR, buf, NULL, NULL,
+			    NULL, 0) > 0) {
+				goto skip_syslog;
+			}
+		}
+	}
+#endif
+
+	SYSLOG ((LOG_WARN, "libselinux: %s", buf));
+
+skip_syslog:
+	free (buf);
+
+	return 0;
+}
+
+/*
+ * check_selinux_permit - Check whether SELinux grants the given
+ *                        operation
+ *
+ *   Parameter is the SELinux permission name, e.g. rootok
+ *
+ *   Returns 0 when permission is granted
+ *                  or something failed but running in
+ *                  permissive mode
+ */
+int check_selinux_permit (const char *perm_name)
+{
+	char *user_context_str;
+	int r;
+
+	if (0 == is_selinux_enabled ()) {
+		return 0;
+	}
+
+	selinux_set_callback (SELINUX_CB_LOG, (union selinux_callback) selinux_log_cb);
+
+	if (getprevcon (&user_context_str) != 0) {
+		fprintf (stderr,
+		    _("%s: can not get previous SELinux process context: %s\n"),
+		    Prog, strerror (errno));
+		SYSLOG ((LOG_WARN,
+		    "can not get previous SELinux process context: %s",
+		    strerror (errno)));
+		return (security_getenforce () != 0);
+	}
+
+	r = selinux_check_access (user_context_str, user_context_str, "passwd", perm_name, NULL);
+	freecon (user_context_str);
+	return r;
+}
+
 #else				/* !WITH_SELINUX */
 extern int errno;		/* warning: ANSI C forbids an empty source file */
 #endif				/* !WITH_SELINUX */

src/Makefile.am

@@ -89,33 +89,33 @@ LIBCRYPT_NOPAM = $(LIBCRYPT)
 endif
 
 chage_LDADD    = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-newuidmap_LDADD    = $(LDADD) $(LIBSELINUX) $(LIBCAP)
+newuidmap_LDADD    = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBCAP)
-newgidmap_LDADD    = $(LDADD) $(LIBSELINUX) $(LIBCAP)
+newgidmap_LDADD    = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBCAP)
-chfn_LDADD     = $(LDADD) $(LIBPAM) $(LIBSELINUX) $(LIBCRYPT_NOPAM) $(LIBSKEY) $(LIBMD) $(LIBECONF)
+chfn_LDADD     = $(LDADD) $(LIBPAM) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT_NOPAM) $(LIBSKEY) $(LIBMD) $(LIBECONF)
-chgpasswd_LDADD = $(LDADD) $(LIBPAM_SUID) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
+chgpasswd_LDADD = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
-chsh_LDADD     = $(LDADD) $(LIBPAM) $(LIBSELINUX) $(LIBCRYPT_NOPAM) $(LIBSKEY) $(LIBMD) $(LIBECONF)
+chsh_LDADD     = $(LDADD) $(LIBPAM) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT_NOPAM) $(LIBSKEY) $(LIBMD) $(LIBECONF)
-chpasswd_LDADD = $(LDADD) $(LIBPAM) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
+chpasswd_LDADD = $(LDADD) $(LIBPAM) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
 expiry_LDADD = $(LDADD) $(LIBECONF)
 gpasswd_LDADD  = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
 groupadd_LDADD = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
 groupdel_LDADD = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-groupmems_LDADD = $(LDADD) $(LIBPAM) $(LIBSELINUX) $(LIBECONF)
+groupmems_LDADD = $(LDADD) $(LIBPAM) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
 groupmod_LDADD = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-grpck_LDADD    = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+grpck_LDADD    = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-grpconv_LDADD  = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+grpconv_LDADD  = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-grpunconv_LDADD = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+grpunconv_LDADD = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
 lastlog_LDADD   = $(LDADD) $(LIBAUDIT) $(LIBECONF)
 login_SOURCES  = \
 	login.c \
 	login_nopam.c
 login_LDADD    = $(LDADD) $(LIBPAM) $(LIBAUDIT) $(LIBCRYPT_NOPAM) $(LIBSKEY) $(LIBMD) $(LIBECONF)
 newgrp_LDADD   = $(LDADD) $(LIBAUDIT) $(LIBCRYPT) $(LIBECONF)
-newusers_LDADD = $(LDADD) $(LIBPAM) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
+newusers_LDADD = $(LDADD) $(LIBPAM) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT) $(LIBECONF)
 nologin_LDADD  =
 passwd_LDADD   = $(LDADD) $(LIBPAM) $(LIBCRACK) $(LIBAUDIT) $(LIBSELINUX) $(LIBCRYPT_NOPAM) $(LIBECONF)
-pwck_LDADD     = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+pwck_LDADD     = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-pwconv_LDADD   = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+pwconv_LDADD   = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
-pwunconv_LDADD = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+pwunconv_LDADD = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
 su_SOURCES     = \
 	su.c \
 	suauth.c
@@ -124,7 +124,7 @@ sulogin_LDADD  = $(LDADD) $(LIBCRYPT) $(LIBECONF)
 useradd_LDADD  = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBSEMANAGE) $(LIBACL) $(LIBATTR) $(LIBECONF)
 userdel_LDADD  = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBSEMANAGE) $(LIBECONF)
 usermod_LDADD  = $(LDADD) $(LIBPAM_SUID) $(LIBAUDIT) $(LIBSELINUX) $(LIBSEMANAGE) $(LIBACL) $(LIBATTR) $(LIBECONF)
-vipw_LDADD     = $(LDADD) $(LIBSELINUX) $(LIBECONF)
+vipw_LDADD     = $(LDADD) $(LIBAUDIT) $(LIBSELINUX) $(LIBECONF)
 
 install-am: all-am
 	$(MAKE) $(AM_MAKEFLAGS) install-exec-am install-data-am

src/chage.c

@@ -48,10 +48,6 @@
 #endif				/* USE_PAM */
 #endif				/* ACCT_TOOLS_SETUID */
 #include <pwd.h>
-#ifdef WITH_SELINUX
-#include <selinux/selinux.h>
-#include <selinux/av_permissions.h>
-#endif
 #include "prototypes.h"
 #include "defines.h"
 #include "pwio.h"
@@ -832,8 +828,8 @@ int main (int argc, char **argv)
 	rgid = getgid ();
 	amroot = (ruid == 0);
 #ifdef WITH_SELINUX
-	if (amroot && (is_selinux_enabled () > 0)) {
+	if (amroot) {
-		amroot = (selinux_check_passwd_access (PASSWD__ROOTOK) == 0);
+		amroot = (check_selinux_permit ("rootok") == 0);
 	}
 #endif
 

src/chfn.c

@@ -40,10 +40,6 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <getopt.h>
-#ifdef WITH_SELINUX
-#include <selinux/selinux.h>
-#include <selinux/av_permissions.h>
-#endif
 #include "defines.h"
 #include "getdef.h"
 #include "nscd.h"
@@ -379,8 +375,7 @@ static void check_perms (const struct passwd *pw)
 	 * check if the change is allowed by SELinux policy.
 	 */
 	if ((pw->pw_uid != getuid ())
-	    && (is_selinux_enabled () > 0)
+	    && (check_selinux_permit ("chfn") != 0)) {
-	    && (selinux_check_passwd_access (PASSWD__CHFN) != 0)) {
 		fprintf (stderr, _("%s: Permission denied.\n"), Prog);
 		closelog ();
 		exit (E_NOPERM);

src/chsh.c

@@ -39,10 +39,6 @@
 #include <pwd.h>
 #include <stdio.h>
 #include <sys/types.h>
-#ifdef WITH_SELINUX
-#include <selinux/selinux.h>
-#include <selinux/av_permissions.h>
-#endif
 #include "defines.h"
 #include "getdef.h"
 #include "nscd.h"
@@ -286,8 +282,7 @@ static void check_perms (const struct passwd *pw)
 	 * check if the change is allowed by SELinux policy.
 	 */
 	if ((pw->pw_uid != getuid ())
-	    && (is_selinux_enabled () > 0)
+	    && (check_selinux_permit("chsh") != 0)) {
-	    && (selinux_check_passwd_access (PASSWD__CHSH) != 0)) {
 		SYSLOG ((LOG_WARN, "can't change shell for '%s'", pw->pw_name));
 		fprintf (stderr,
 		         _("You may not change the shell for '%s'.\n"),

src/passwd.c

@@ -41,12 +41,6 @@
 #include <signal.h>
 #include <stdio.h>
 #include <sys/types.h>
-#ifdef WITH_SELINUX
-#include <selinux/selinux.h>
-#include <selinux/flask.h>
-#include <selinux/av_permissions.h>
-#include <selinux/context.h>
-#endif				/* WITH_SELINUX */
 #include <time.h>
 #include "defines.h"
 #include "getdef.h"
@@ -149,11 +143,6 @@ static char *update_crypt_pw (char *);
 static void update_noshadow (void);
 
 static void update_shadow (void);
-#ifdef WITH_SELINUX
-static int check_selinux_access (const char *changed_user,
-                                 uid_t changed_uid,
-                                 access_vector_t requested_access);
-#endif				/* WITH_SELINUX */
 
 /*
  * usage - print command usage and exit
@@ -710,55 +699,6 @@ static void update_shadow (void)
 	spw_locked = false;
 }
 
-#ifdef WITH_SELINUX
-static int check_selinux_access (const char *changed_user,
-                                 uid_t changed_uid,
-                                 access_vector_t requested_access)
-{
-	int status = -1;
-	security_context_t user_context;
-	context_t c;
-	const char *user;
-
-	/* if in permissive mode then allow the operation */
-	if (security_getenforce() == 0) {
-		return 0;
-	}
-
-	/* get the context of the process which executed passwd */
-	if (getprevcon(&user_context) != 0) {
-		return -1;
-	}
-
-	/* get the "user" portion of the context (the part before the first
-	   colon) */
-	c = context_new(user_context);
-	user = context_user_get(c);
-
-	/* if changing a password for an account with UID==0 or for an account
-	   where the identity matches then return success */
-	if (changed_uid != 0 && strcmp(changed_user, user) == 0) {
-		status = 0;
-	} else {
-		struct av_decision avd;
-		int retval;
-		retval = security_compute_av(user_context,
-		                             user_context,
-		                             SECCLASS_PASSWD,
-		                             requested_access,
-		                             &avd);
-		if ((retval == 0) &&
-		    ((requested_access & avd.allowed) == requested_access)) {
-			status = 0;
-		}
-	}
-	context_free(c);
-	freecon(user_context);
-	return status;
-}
-
-#endif				/* WITH_SELINUX */
-
 /*
  * passwd - change a user's password file information
  *
@@ -1034,22 +974,13 @@ int main (int argc, char **argv)
 #ifdef WITH_SELINUX
 	/* only do this check when getuid()==0 because it's a pre-condition for
 	   changing a password without entering the old one */
-	if ((is_selinux_enabled() > 0) && (getuid() == 0) &&
+	if (amroot && (check_selinux_permit ("passwd") != 0)) {
-	    (check_selinux_access (name, pw->pw_uid, PASSWD__PASSWD) != 0)) {
-		security_context_t user_context = NULL;
-		const char *user = "Unknown user context";
-		if (getprevcon (&user_context) == 0) {
-			user = user_context; /* FIXME: use context_user_get? */
-		}
 		SYSLOG ((LOG_ALERT,
-		         "%s is not authorized to change the password of %s",
+		         "root is not authorized by SELinux to change the password of %s",
-		         user, name));
+		         name));
 		(void) fprintf(stderr,
-		               _("%s: %s is not authorized to change the password of %s\n"),
+		               _("%s: root is not authorized by SELinux to change the password of %s\n"),
-		               Prog, user, name);
+		               Prog, name);
-		if (NULL != user_context) {
-			freecon (user_context);
-		}
 		exit (E_NOPERM);
 	}
 #endif				/* WITH_SELINUX */