[master] Fixed relative file name crash

Merges in rt46957

RELNOTES

@@ -103,6 +103,13 @@ by Eric Young (eay@cryptsoft.com).
   cannot rely on the results of executable statements.
   [ISC-Bugs #45451]
 
+- Fixed a bug which causes dhcpd and dhclient to crash on certain
+  systems when given relative path names for lease or pid files on
+  the command line.  Affected systems are those on which the C library
+  function, realpath() does not support a second parameter value of
+  NULL (see manpages for realpath(3)).
+  [ISC-Bugs #46957]
+
 		Changes since 4.4.0a1 (New Features)
 
 - Added experimental support for relay port (draft-ietf-dhc-relay-port-10.txt)

client/dhclient.c

@@ -639,17 +639,11 @@ main(int argc, char **argv) {
 	 * to be reopened after chdir() has been called
 	 */
 	if (path_dhclient_db[0] != '/') {
-		const char *old_path = path_dhclient_db;
+		path_dhclient_db = absolute_path(path_dhclient_db);
-		path_dhclient_db = realpath(path_dhclient_db, NULL);
-		if (path_dhclient_db == NULL)
-			log_fatal("Failed to get realpath for %s: %s", old_path, strerror(errno));
 	}
 
 	if (path_dhclient_script[0] != '/') {
-		const char *old_path = path_dhclient_script;
+		path_dhclient_script = absolute_path(path_dhclient_script);
-		path_dhclient_script = realpath(path_dhclient_script, NULL);
-		if (path_dhclient_script == NULL)
-			log_fatal("Failed to get realpath for %s: %s", old_path, strerror(errno));
 	}
 
 	/*

common/print.c

@@ -3,7 +3,7 @@
    Turn data structures into printable text. */
 
 /*
- * Copyright (c) 2004-2017 by Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (c) 2004-2018 by Internet Systems Consortium, Inc. ("ISC")
  * Copyright (c) 1995-2003 by Internet Software Consortium
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
@@ -1439,3 +1439,43 @@ char *format_lease_id(const unsigned char *s, unsigned len,
 	}
 	return (idstr);
 }
+
+/*
+ * Convert a relative path name to an absolute path name
+ *
+ * Not all versions of realpath() support NULL for
+ * the second parameter and PATH_MAX isn't defined
+ * on all systems.  For the latter, we'll make what
+ * ought to be a big enough buffer and let it fly.
+ * If passed an absolute path it should return it
+ * an allocated buffer.
+ */
+char *absolute_path(const char *orgpath) {
+	char *abspath = NULL;
+	if (orgpath) {
+#ifdef PATH_MAX
+		char buf[PATH_MAX];
+#else
+		char buf[2048];
+		int len;
+#endif
+		errno = 0;
+                if (realpath(orgpath, buf) == NULL) {
+			const char* errmsg = strerror(errno);
+                        log_fatal("Failed to get realpath for %s: %s",
+				  orgpath, errmsg);
+		}
+
+		/* dup the result into an allocated buffer */
+		abspath = dmalloc(strlen(buf) + 1, MDL);
+		if (abspath == NULL)  {
+			log_fatal("No memory for filename:%s\n",
+				  buf);
+		}
+
+		memcpy (abspath, buf, strlen(buf));
+		abspath[strlen(buf)] = 0x0;
+	}
+
+	return (abspath);
+}

includes/dhcpd.h

@@ -2635,6 +2635,7 @@ char *buf_to_hex (const unsigned char *s, unsigned len,
                    const char *file, int line);
 char *format_lease_id(const unsigned char *s, unsigned len, int format,
                       const char *file, int line);
+char *absolute_path(const char *orgpath);
 /* socket.c */
 #if defined (USE_SOCKET_SEND) || defined (USE_SOCKET_RECEIVE) \
 	|| defined (USE_SOCKET_FALLBACK)

server/dhcpd.c

@@ -607,11 +607,7 @@ main(int argc, char **argv) {
          * to be reopened after chdir() has been called
          */
         if (have_dhcpd_db && path_dhcpd_db[0] != '/') {
-		const char *path = path_dhcpd_db;
+                path_dhcpd_db = absolute_path(path_dhcpd_db);
-                path_dhcpd_db = realpath(path_dhcpd_db, NULL);
-                if (path_dhcpd_db == NULL)
-                        log_fatal("Failed to get realpath for %s: %s", path,
-                                   strerror(errno));
         }
 
 	if (!quiet) {