if port 20 incoming, kill it and try again

1 files changed, 9 insertions, 0 deletions

diff --git a/src/lib/libc/net/rcmd.c b/src/lib/libc/net/rcmd.c
index 643604f3b3..86f35664e4 100644
--- a/src/lib/libc/net/rcmd.c
+++ b/src/lib/libc/net/rcmd.c
@@ -153,6 +153,7 @@ rcmd(ahost, rport, locuser, remuser, cmd, fd2p)
                         (void)close(s2);
                         goto bad;
                 }
+again:
                 FD_ZERO(&reads);
                 FD_SET(s, &reads);
                 FD_SET(s2, &reads);
@@ -170,6 +171,14 @@ rcmd(ahost, rport, locuser, remuser, cmd, fd2p)
                         goto bad;
                 }
                 s3 = accept(s2, (struct sockaddr *)&from, &len);
+                /*
+                 * XXX careful for ftp bounce attacks. If discovered, shut them
+                 * down and check for the real auxiliary channel to connect.
+                 */
+                if (from.sin_family == AF_INET && from.sin_port == htons(20)) {
+                        close(s3);
+                        goto again;
+                }
                 (void)close(s2);
                 if (s3 < 0) {
                         (void)fprintf(stderr,