Integrate the functionality from runscript_selinux.so

runscript used to dlopen() runscript_selinux.so. This adds equivalent
functionality directly in to runscript instead. It authenticates with
either PAM or shadow and optionally has a dep on audit.

X-Gentoo-Bug: 517450
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=517450

3 files changed, 265 insertions, 31 deletions

diff --git a/src/rc/rc-selinux.c b/src/rc/rc-selinux.c
index 518b25df..7124e83e 100644
--- a/src/rc/rc-selinux.c
+++ b/src/rc/rc-selinux.c
@@ -1,7 +1,7 @@
 /*
-  rc-selinux.c
-  SELinux helpers to get and set contexts.
-*/
+ * rc-selinux.c
+ * SELinux helpers to get and set contexts.
+ */
 
 /*
  * Copyright (c) 2014 Jason Zaman <jason@perfinion.com>
@@ -31,11 +31,18 @@
 #include <stddef.h>
 #include <errno.h>
 #include <dlfcn.h>
-
-#include <sys/stat.h>
+#include <ctype.h>
+#include <limits.h>
+#include <pwd.h>
+#include <unistd.h>
 
 #include <selinux/selinux.h>
 #include <selinux/label.h>
+#include <selinux/get_default_type.h>
+#include <selinux/context.h>
+
+#include <sys/stat.h>
+#include <sys/types.h>
 
 #include "einfo.h"
 #include "queue.h"
@@ -44,11 +51,28 @@
 #include "rc-plugin.h"
 #include "rc-selinux.h"
 
-#define SELINUX_LIB     RC_LIBDIR "/runscript_selinux.so"
+/* the context files for selinux */
+#define RUN_INIT_FILE "run_init_type"
+#define INITRC_FILE "initrc_context"
 
-static void (*selinux_run_init_old) (void);
-static void (*selinux_run_init_new) (int argc, char **argv);
+#ifdef HAVE_AUDIT
+#include <libaudit.h>
+#endif
 
+/* PAM or shadow for authentication */
+#ifdef HAVE_PAM
+#    define PAM_SERVICE_NAME "run_init" /* the name of this program for PAM */
+#    include <security/pam_appl.h>
+#    include <security/pam_misc.h>
+#else
+#    define PASSWORD_PROMPT "Password:"
+#    include <crypt.h>
+#    include <shadow.h>
+#    include <string.h>
+#endif
+
+
+/* The handle for the fcontext lookups */
 static struct selabel_handle *hnd = NULL;
 
 int selinux_util_label(const char *path)
@@ -133,33 +157,243 @@ int selinux_util_close(void)
 	return 0;
 }
 
-void selinux_setup(int argc, char **argv)
+/*
+ * This will check the users password and return 0 on success or -1 on fail
+ *
+ * We ask for the password to make sure it is intended vs run by malicious software.
+ * Actual authorization is covered by the policy itself.
+ */
+static int check_password(char *username)
 {
-	void *lib_handle = NULL;
+	int ret = 1;
+#ifdef HAVE_PAM
+	pam_handle_t *pamh;
+	int pam_err = 0;
+	const struct pam_conv pconv = {
+		misc_conv,
+		NULL
+	};
 
-	if (!exists(SELINUX_LIB))
-		return;
+	pam_err = pam_start(PAM_SERVICE_NAME, username, &pconv, &pamh);
+	if (pam_err != PAM_SUCCESS) {
+		ret = -1;
+		goto outpam;
+	}
 
-	lib_handle = dlopen(SELINUX_LIB, RTLD_NOW | RTLD_GLOBAL);
-	if (!lib_handle) {
-		eerror("dlopen: %s", dlerror());
-		return;
+	pam_err = pam_authenticate(pamh, PAM_DISALLOW_NULL_AUTHTOK);
+	if (pam_err != PAM_SUCCESS) {
+		ret = -1;
+		goto outpam;
+	}
+
+	ret = 0;
+outpam:
+	pam_end(pamh, pam_err);
+	pamh = NULL;
+
+#else /* authenticating via /etc/shadow instead */
+	struct spwd *spw;
+	char *password;
+	char *attempt;
+
+	spw = getspnam(username);
+	if (!spw) {
+		eerror("Failed to read shadow entry");
+		ret = -1;
+		goto outshadow;
+	}
+
+	attempt = getpass(PASSWORD_PROMPT);
+	if (!attempt) {
+		ret = -1;
+		goto outshadow;
+	}
+
+	if (*spw->sp_pwdp == '\0' && *attempt == '\0') {
+		ret = -1;
+		goto outshadow;
+	}
+
+	/* salt must be at least two characters long */
+	if (!(spw->sp_pwdp[0] && spw->sp_pwdp[1])) {
+		ret = -1;
+		goto outshadow;
 	}
 
-	selinux_run_init_old = (void (*)(void))
-	    dlfunc(lib_handle, "selinux_runscript");
-	selinux_run_init_new = (void (*)(int, char **))
-	    dlfunc(lib_handle, "selinux_runscript2");
+	/* encrypt the password attempt */
+	password = crypt(attempt, spw->sp_pwdp);
 
-	/* Use new run_init if it exists, else fall back to old */
-	if (selinux_run_init_new)
-		selinux_run_init_new(argc, argv);
-	else if (selinux_run_init_old)
-		selinux_run_init_old();
+	if (password && strcmp(password, spw->sp_pwdp) == 0)
+		ret = 0;
 	else
-		/* This shouldnt happen... probably corrupt lib */
-		eerrorx
-		    ("run_init is missing from runscript_selinux.so!");
+		ret = -1;
+outshadow:
+#endif
+	return ret;
+}
+
+/* Authenticates the user, returns 0 on success, 1 on fail */
+static int check_auth()
+{
+	struct passwd *pw;
+	uid_t uid;
+
+#ifdef HAVE_AUDIT
+	uid = audit_getloginuid();
+	if (uid == (uid_t) -1)
+		uid = getuid();
+#else
+	uid = getuid();
+#endif
+
+	pw = getpwuid(uid);
+	if (!pw) {
+		eerror("cannot find your entry in the passwd file.");
+		return (-1);
+	}
+
+	printf("Authenticating %s.\n", pw->pw_name);
+
+	/* do the actual check */
+	if (check_password(pw->pw_name) == 0) {
+		return 0;
+	}
+
+	eerrorx("Authentication failed for %s", pw->pw_name);
+	return 1;
+}
+
+/*
+ * Read the context from the given context file. context must be free'd by the user.
+ */
+static int read_context_file(const char *filename, char **context)
+{
+	int ret = -1;
+	FILE *fp;
+	char filepath[PATH_MAX];
+	char *line = NULL;
+	char *p;
+	char *p2;
+	size_t len = 0;
+	ssize_t read;
+
+	memset(filepath, '\0', PATH_MAX);
+	snprintf(filepath, PATH_MAX - 1, "%s/%s", selinux_contexts_path(), filename);
+
+	fp = fopen(filepath, "r");
+	if (fp == NULL) {
+		eerror("Failed to open context file: %s", filename);
+		return -1;
+	}
+
+	while ((read = getline(&line, &len, fp)) != -1) {
+		/* cut off spaces before the string */
+		p = line;
+		while (isspace(*p) && *p != '\0')
+			p++;
+
+		/* empty string, skip */
+		if (*p == '\0')
+			continue;
+
+		/* cut off spaces after the string */
+		p2 = p;
+		while (!isspace(*p2) && *p2 != '\0')
+			p2++;
+		*p2 = '\0';
+
+		*context = xstrdup(p);
+		ret = 0;
+		break;
+	}
+
+	free(line);
+	fclose(fp);
+	return ret;
+}
+
+void selinux_setup(char **argv)
+{
+	char *new_context = NULL;
+	char *curr_context = NULL;
+	context_t curr_con;
+	char *curr_t = NULL;
+	char *run_init_t = NULL;
+
+	/* Return, if selinux is disabled. */
+	if (is_selinux_enabled() < 1) {
+		return;
+	}
+
+	if (read_context_file(RUN_INIT_FILE, &run_init_t) != 0) {
+		/* assume a reasonable default, rather than bailing out */
+		run_init_t = xstrdup("run_init_t");
+		ewarn("Assuming SELinux run_init type is %s", run_init_t);
+	}
+
+	/* Get our current context. */
+	if (getcon(&curr_context) < 0) {
+		if (errno == ENOENT) {
+			/* should only hit this if proc is not mounted.  this
+			 * happens on Gentoo right after init starts, when
+			 * the init script processing starts.
+			 */
+			goto out;
+		} else {
+			perror("getcon");
+			exit(1);
+		}
+	}
+
+	/* extract the type from the context */
+	curr_con = context_new(curr_context);
+	curr_t = xstrdup(context_type_get(curr_con));
+	/* dont need them anymore so free() now */
+	context_free(curr_con);
+	free(curr_context);
+
+	/* if we are not in the run_init domain, we should not do anything */
+	if (strncmp(run_init_t, curr_t, strlen(run_init_t)) != 0) {
+		goto out;
+	}
+
+	free(curr_t);
+	free(run_init_t);
+
+	if (check_auth() != 0) {
+		eerrorx("Authentication failed.");
+	}
+
+	/* Get the context for the script to be run in. */
+	if (read_context_file(INITRC_FILE, &new_context) != 0) {
+		/* assume a reasonable default, rather than bailing out */
+		new_context = xstrdup("system_u:system_r:initrc_t");
+		ewarn("Assuming SELinux initrc context is %s", new_context);
+	}
+
+	/* Set the new context */
+	if (setexeccon(new_context) < 0) {
+		eerrorx("Could not set SELinux exec context to %s.", new_context);
+	}
+
+	free(new_context);
+
+	/*
+	 * exec will recycle ptys so try and use open_init_pty if it exists
+	 * which will open the pty with initrc_devpts_t, if it doesnt exist,
+	 * fall back to plain exec
+	 */
+	if (access("/usr/sbin/open_init_pty", X_OK)) {
+		if (execvp("/usr/sbin/open_init_pty", argv)) {
+			perror("execvp");
+			exit(-1);
+		}
+	} else if (execvp(argv[1], argv + 1)) {
+		perror("execvp");
+		exit(-1);
+	}
 
-	dlclose(lib_handle);
+out:
+	free(run_init_t);
+	free(curr_t);
 }
diff --git a/src/rc/rc-selinux.h b/src/rc/rc-selinux.h
index 8cf73b05..e28f3339 100644
--- a/src/rc/rc-selinux.h
+++ b/src/rc/rc-selinux.h
@@ -30,6 +30,6 @@ int selinux_util_open(void);
 int selinux_util_label(const char *path);
 int selinux_util_close(void);
 
-void selinux_setup(int argc, char **argv);
+void selinux_setup(char **argv);
 
 #endif
diff --git a/src/rc/runscript.c b/src/rc/runscript.c
index 882cb8c0..0ac19661 100644
--- a/src/rc/runscript.c
+++ b/src/rc/runscript.c
@@ -1193,7 +1193,7 @@ openrc_run(int argc, char **argv)
 
 #ifdef HAVE_SELINUX
 	/* Ok, we are ready to go, so setup selinux if applicable */
-	selinux_setup(argc, argv);
+	selinux_setup(argv);
 #endif
 
 	deps = true;