Fix coverity unbound buffer issues

During coverity scan, there is reported an issue
with unbounded source buffer for each usage of input arg
directly with syslog function.
This commit is to limit the names of users and groups
passed as input args to a fixed value of 256.
The max length 256 is a typical POSIX login name length.
This should improve also security.

lib/alloc.c

@@ -71,3 +71,23 @@ xreallocarray(void *p, size_t nmemb, size_t size)
 	        log_get_progname(), strerror(errno));
 	exit(13);
 }
+
+char *
+xstrndup(const char *s, size_t max_length) {
+    size_t length = strlen(s);
+    if (length > max_length) {
+        length = max_length;
+    }
+
+    char *p = malloc(length + 1);
+    if (!p) {
+		fprintf(log_get_logfd(), _("%s: %s\n"),
+	    		log_get_progname(), strerror(errno));
+        exit(13);
+    }
+
+    strncpy(p, s, length);
+    p[length] = '\0';
+
+    return p;
+}

lib/alloc.h

@@ -55,6 +55,8 @@ void *xcalloc(size_t nmemb, size_t size);
 ATTR_MALLOC(free)
 void *xreallocarray(void *p, size_t nmemb, size_t size);
 
+ATTR_MALLOC(free)
+char *xstrndup(const char *s, size_t max_length);
 
 inline void *
 xmalloc(size_t size)

lib/defines.h

@@ -213,4 +213,13 @@
 #define PASS_MAX  BUFSIZ - 1
 #endif
 
+/* Maximum length of user name or group name
+ * This is used only to limit a string length passed to syslog.
+ * An issue "unbounded source buffer" is reported while doing 
+ * coverity scans, when there is an unlimited string length passed 
+ * to syslog function.
+ * Typical POSIX login name max length is 256.
+ */
+#define USER_ENTRY_MAX_LENGTH 256
+
 #endif				/* _DEFINES_H_ */

src/chfn.c

@@ -648,7 +648,7 @@ int main (int argc, char **argv)
 	 * name, or the name getlogin() returns.
 	 */
 	if (optind < argc) {
-		user = argv[optind];
+		user = xstrndup(argv[optind], USER_ENTRY_MAX_LENGTH);
 		pw = xgetpwnam (user);
 		if (NULL == pw) {
 			fprintf (stderr, _("%s: user '%s' does not exist\n"), Prog,

src/chsh.c

@@ -498,7 +498,7 @@ int main (int argc, char **argv)
 	 * name, or the name getlogin() returns.
 	 */
 	if (optind < argc) {
-		user = argv[optind];
+		user = xstrndup(argv[optind], USER_ENTRY_MAX_LENGTH);
 		pw = xgetpwnam (user);
 		if (NULL == pw) {
 			fprintf (stderr,

src/newgrp.c

@@ -482,7 +482,7 @@ int main (int argc, char **argv)
 		 * not "newgrp".
 		 */
 		if ((argc > 0) && (argv[0][0] != '-')) {
-			group = argv[0];
+			group = xstrndup(argv[0], USER_ENTRY_MAX_LENGTH);
 			argc--;
 			argv++;
 		} else {
@@ -513,7 +513,7 @@ int main (int argc, char **argv)
 			usage ();
 			goto failure;
 		} else if (argv[0] != NULL) {
-			group = argv[0];
+			group = xstrndup(argv[0], USER_ENTRY_MAX_LENGTH);
 		} else {
 			/*
 			 * get the group file entry for her login group id.

src/passwd.c

@@ -907,7 +907,7 @@ int main (int argc, char **argv)
 	}
 	myname = xstrdup (pw->pw_name);
 	if (optind < argc) {
-		name = argv[optind];
+		name = xstrndup(argv[optind], USER_ENTRY_MAX_LENGTH);
 	} else {
 		name = myname;
 	}