- Fix for #303 CVE-2020-28935 : Fix that symlink does not interfere

with chown of pidfile.

daemon/unbound.c

@@ -341,18 +341,32 @@ readpid (const char* file)
 static void
 writepid (const char* pidfile, pid_t pid)
 {
-	FILE* f;
+	int fd;
+	char pidbuf[32];
+	size_t count = 0;
+	snprintf(pidbuf, sizeof(pidbuf), "%lu\n", (unsigned long)pid);
 
-	if ((f = fopen(pidfile, "w")) ==  NULL ) {
+	if((fd = open(pidfile, O_WRONLY | O_CREAT | O_TRUNC
+#ifdef O_NOFOLLOW
+		| O_NOFOLLOW
+#endif
+		, 0644)) == -1) {
 		log_err("cannot open pidfile %s: %s", 
 			pidfile, strerror(errno));
 		return;
 	}
-	if(fprintf(f, "%lu\n", (unsigned long)pid) < 0) {
-		log_err("cannot write to pidfile %s: %s", 
-			pidfile, strerror(errno));
+	while(count < strlen(pidbuf)) {
+		ssize_t r = write(fd, pidbuf+count, strlen(pidbuf)-count);
+		if(r == -1) {
+			if(errno == EAGAIN || errno == EINTR)
+				continue;
+			log_err("cannot write to pidfile %s: %s",
+				pidfile, strerror(errno));
+			break;
+		}
+		count += r;
 	}
-	fclose(f);
+	close(fd);
 }
 
 /**

doc/Changelog

@@ -6,6 +6,8 @@
 	  supported by protocol.
 	- Fix #347: IP_DONTFRAG broken on Apple xcode 12.2.
 	- Option to toggle udp-connect, default is enabled.
+	- Fix for #303 CVE-2020-28935 : Fix that symlink does not interfere
+	  with chown of pidfile.
 
 12 November 2020: Wouter
 	- Fix to connect() to UDP destinations, default turned on,