Added leading comment and security check.
diff --git a/Demo/pysvr/pysvr.c b/Demo/pysvr/pysvr.c
index f6f9e08..133b785 100644
--- a/Demo/pysvr/pysvr.c
+++ b/Demo/pysvr/pysvr.c
@@ -1,3 +1,13 @@
+/* A multi-threaded telnet-like server that gives a Python prompt.
+
+Usage: pysvr [port]
+
+For security reasons, it only accepts requests from the current host.
+This can still be insecure, but restricts violations from people who
+can log in on your machine. Use with caution!
+
+*/
+
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -88,8 +98,8 @@
static void
main_thread(int port)
{
- int sock;
- struct sockaddr_in addr;
+ int sock, conn, size;
+ struct sockaddr_in addr, clientaddr;
sock = socket(PF_INET, SOCK_STREAM, 0);
if (sock < 0) {
@@ -117,9 +127,7 @@
fprintf(stderr, "Listening on port %d...\n", port);
for (;;) {
- struct sockaddr_in clientaddr;
- int conn, size;
-
+ size = sizeof clientaddr;
conn = accept(sock, (struct sockaddr *) &clientaddr, &size);
if (conn < 0) {
oprogname();
@@ -127,6 +135,21 @@
exit(1);
}
+ size = sizeof addr;
+ if (getsockname(conn, (struct sockaddr *)&addr, &size) < 0) {
+ oprogname();
+ perror("can't get socket name of connection");
+ exit(1);
+ }
+ if (clientaddr.sin_addr.s_addr != addr.sin_addr.s_addr) {
+ oprogname();
+ perror("connection from non-local host refused");
+ fprintf(stderr, "(addr=%lx, clientaddr=%lx)\n",
+ ntohl(addr.sin_addr.s_addr),
+ ntohl(clientaddr.sin_addr.s_addr));
+ close(conn);
+ continue;
+ }
create_thread(conn, &clientaddr);
}
}