Skip passwords longer than 1k in length so clients can't easily DoS sshd

by sending very long passwords, causing it to spend CPU hashing them.
feedback djm@, ok markus@.

Brought to our attention by tomas.kuthan at oracle.com, shilei-c at
360.cn and coredump at autistici.org

diff --git a/usr.bin/ssh/auth-passwd.c b/usr.bin/ssh/auth-passwd.c
index 1346f8c..69f49bf 100644 (file)
--- a/usr.bin/ssh/auth-passwd.c
+++ b/usr.bin/ssh/auth-passwd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-passwd.c,v 1.44 2014/07/15 15:54:14 millert Exp $ */
+/* $OpenBSD: auth-passwd.c,v 1.45 2016/07/21 01:39:35 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -63,6 +63,8 @@ extern login_cap_t *lc;
 #define DAY            (24L * 60 * 60) /* 1 day in seconds */
 #define TWO_WEEKS      (2L * 7 * DAY)  /* 2 weeks in seconds */
 
+#define MAX_PASSWORD_LEN       1024
+
 static void
 disable_forwarding(void)
 {
@@ -81,6 +83,9 @@ auth_password(Authctxt *authctxt, const char *password)
        struct passwd * pw = authctxt->pw;
        int ok = authctxt->valid;
 
+       if (strlen(password) > MAX_PASSWORD_LEN)
+               return 0;
+
        if (pw->pw_uid == 0 && options.permit_root_login != PERMIT_YES)
                ok = 0;
        if (*password == '\0' && options.permit_empty_passwd == 0)