Move check_user_in_passwd from pam_localuser.c to pam_modutil

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

* modules/pam_localuser/pam_localuser.c: Include
<security/pam_modutil.h>.
(pam_sm_authenticate): Replace check_user_in_passwd with
pam_modutil_check_user_in_passwd.
(check_user_in_passwd): Rename to pam_modutil_check_user_in_passwd,
move to ...
* libpam/pam_modutil_check_user.c: ... new file.
* libpam/Makefile.am (libpam_la_SOURCES): Add pam_modutil_check_user.c.
* libpam/include/security/pam_modutil.h
(pam_modutil_check_user_in_passwd): New function declaration.
* libpam/libpam.map (LIBPAM_MODUTIL_1.4.1): New interface.

Co-authored-by: Dmitry V. Levin <ldv@altlinux.org>

4 files changed, 101 insertions, 0 deletions

diff --git a/libpam/Makefile.am b/libpam/Makefile.am
index 9252a837..11a1f329 100644
--- a/libpam/Makefile.am
+++ b/libpam/Makefile.am
@@ -35,6 +35,7 @@ libpam_la_SOURCES = pam_account.c pam_auth.c pam_data.c pam_delay.c \
 	pam_misc.c pam_password.c pam_prelude.c \
 	pam_session.c pam_start.c pam_strerror.c \
 	pam_vprompt.c pam_syslog.c pam_dynamic.c pam_audit.c \
+	pam_modutil_check_user.c \
 	pam_modutil_cleanup.c pam_modutil_getpwnam.c pam_modutil_ioloop.c \
 	pam_modutil_getgrgid.c pam_modutil_getpwuid.c pam_modutil_getgrnam.c \
 	pam_modutil_getspnam.c pam_modutil_getlogin.c pam_modutil_ingroup.c \
diff --git a/libpam/include/security/pam_modutil.h b/libpam/include/security/pam_modutil.h
index 3a6aec6a..33f87b90 100644
--- a/libpam/include/security/pam_modutil.h
+++ b/libpam/include/security/pam_modutil.h
@@ -58,6 +58,11 @@ extern "C" {
 
 #include <security/_pam_types.h>
 
+extern int PAM_NONNULL((1,2))
+pam_modutil_check_user_in_passwd(pam_handle_t *pamh,
+                                 const char *user_name,
+                                 const char *file_name);
+
 extern struct passwd * PAM_NONNULL((1,2))
 pam_modutil_getpwnam(pam_handle_t *pamh, const char *user);
 
diff --git a/libpam/libpam.map b/libpam/libpam.map
index c9690a91..3cc7ef35 100644
--- a/libpam/libpam.map
+++ b/libpam/libpam.map
@@ -82,3 +82,8 @@ LIBPAM_1.4 {
   global:
     pam_start_confdir;
 } LIBPAM_1.0;
+
+LIBPAM_MODUTIL_1.4.1 {
+  global:
+    pam_modutil_check_user_in_passwd;
+} LIBPAM_MODUTIL_1.3.2;
diff --git a/libpam/pam_modutil_check_user.c b/libpam/pam_modutil_check_user.c
new file mode 100644
index 00000000..898b13a9
--- /dev/null
+++ b/libpam/pam_modutil_check_user.c
@@ -0,0 +1,90 @@
+#include "pam_modutil_private.h"
+#include <security/pam_ext.h>
+
+#include <stdio.h>
+#include <string.h>
+#include <syslog.h>
+
+int
+pam_modutil_check_user_in_passwd(pam_handle_t *pamh,
+				 const char *user_name,
+				 const char *file_name)
+{
+	int rc;
+	size_t user_len;
+	FILE *fp;
+	char line[BUFSIZ];
+
+	/* Validate the user name.  */
+	if ((user_len = strlen(user_name)) == 0) {
+		pam_syslog(pamh, LOG_NOTICE, "user name is not valid");
+		return PAM_SERVICE_ERR;
+	}
+
+	if (user_len > sizeof(line) - sizeof(":")) {
+		pam_syslog(pamh, LOG_NOTICE, "user name is too long");
+		return PAM_SERVICE_ERR;
+	}
+
+	if (strchr(user_name, ':') != NULL) {
+		/*
+		 * "root:x" is not a local user name even if the passwd file
+		 * contains a line starting with "root:x:".
+		 */
+		return PAM_PERM_DENIED;
+	}
+
+	/* Open the passwd file.  */
+	if (file_name == NULL) {
+		file_name = "/etc/passwd";
+	}
+	if ((fp = fopen(file_name, "r")) == NULL) {
+		pam_syslog(pamh, LOG_ERR, "error opening %s: %m", file_name);
+		return PAM_SERVICE_ERR;
+	}
+
+	/*
+	 * Scan the file using fgets() instead of fgetpwent_r() because
+	 * the latter is not flexible enough in handling long lines
+	 * in passwd files.
+	 */
+	rc = PAM_PERM_DENIED;
+	while (fgets(line, sizeof(line), fp) != NULL) {
+		size_t line_len;
+		const char *str;
+
+		/*
+		 * Does this line start with the user name
+		 * followed by a colon?
+		 */
+		if (strncmp(user_name, line, user_len) == 0 &&
+		    line[user_len] == ':') {
+			rc = PAM_SUCCESS;
+			break;
+		}
+		/* Has a newline been read?  */
+		line_len = strlen(line);
+		if (line_len < sizeof(line) - 1 ||
+		    line[line_len - 1] == '\n') {
+			/* Yes, continue with the next line.  */
+			continue;
+		}
+
+		/* No, read till the end of this line first.  */
+		while ((str = fgets(line, sizeof(line), fp)) != NULL) {
+			line_len = strlen(line);
+			if (line_len == 0 ||
+			    line[line_len - 1] == '\n') {
+				break;
+			}
+		}
+		if (str == NULL) {
+			/* fgets returned NULL, we are done.  */
+			break;
+		}
+		/* Continue with the next line.  */
+	}
+
+	fclose(fp);
+	return rc;
+}