From 46b22e57d91e33a591d0fba97da52672af4d6ed2 Mon Sep 17 00:00:00 2001
From: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
Date: Mon, 29 May 2017 10:25:09 +0100
Subject: [PATCH] dropbear server: support -T max auth tries

Add support for '-T n' for a run-time specification for maximum number
of authentication attempts where 'n' is between 1 and compile time
option MAX_AUTH_TRIES.

A default number of tries can be specified at compile time using
'DEFAULT_AUTH_TRIES' which itself defaults to MAX_AUTH_TRIES for
backwards compatibility.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
---
 options.h     |  7 +++++++
 runopts.h     |  1 +
 svr-auth.c    |  2 +-
 svr-runopts.c | 17 +++++++++++++++++
 4 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/options.h b/options.h
index 0c51bb1..4d22704 100644
--- a/options.h
+++ b/options.h
@@ -284,6 +284,13 @@ Homedir is prepended unless path begins with / */
 #define MAX_AUTH_TRIES 10
 #endif
 
+/* Default maximum number of failed authentication tries.
+ * defaults to MAX_AUTH_TRIES */
+
+#ifndef DEFAULT_AUTH_TRIES
+#define DEFAULT_AUTH_TRIES MAX_AUTH_TRIES
+#endif
+
 /* The default file to store the daemon's process ID, for shutdown
    scripts etc. This can be overridden with the -P flag */
 #ifndef DROPBEAR_PIDFILE
diff --git a/runopts.h b/runopts.h
index f7c869d..2f7da63 100644
--- a/runopts.h
+++ b/runopts.h
@@ -96,6 +96,7 @@ typedef struct svr_runopts {
 	int noauthpass;
 	int norootpass;
 	int allowblankpass;
+	unsigned int maxauthtries;
 
 #ifdef ENABLE_SVR_REMOTETCPFWD
 	int noremotetcp;
diff --git a/svr-auth.c b/svr-auth.c
index 577ea88..6a7ce0b 100644
--- a/svr-auth.c
+++ b/svr-auth.c
@@ -362,7 +362,7 @@ void send_msg_userauth_failure(int partial, int incrfail) {
 		ses.authstate.failcount++;
 	}
 
-	if (ses.authstate.failcount >= MAX_AUTH_TRIES) {
+	if (ses.authstate.failcount >= svr_opts.maxauthtries) {
 		char * userstr;
 		/* XXX - send disconnect ? */
 		TRACE(("Max auth tries reached, exiting"))
diff --git a/svr-runopts.c b/svr-runopts.c
index 8f60059..1e7440f 100644
--- a/svr-runopts.c
+++ b/svr-runopts.c
@@ -73,6 +73,7 @@ static void printhelp(const char * progname) {
 					"-g		Disable password logins for root\n"
 					"-B		Allow blank password logins\n"
 #endif
+					"-T <1 to %d> 	Maximum authentication tries (default %d)\n"
 #ifdef ENABLE_SVR_LOCALTCPFWD
 					"-j		Disable local port forwarding\n"
 #endif
@@ -106,6 +107,7 @@ static void printhelp(const char * progname) {
 #ifdef DROPBEAR_ECDSA
 					ECDSA_PRIV_FILENAME,
 #endif
+					MAX_AUTH_TRIES, DEFAULT_AUTH_TRIES,
 					DROPBEAR_MAX_PORTS, DROPBEAR_DEFPORT, DROPBEAR_PIDFILE,
 					DEFAULT_RECV_WINDOW, DEFAULT_KEEPALIVE, DEFAULT_IDLE_TIMEOUT);
 }
@@ -118,6 +120,7 @@ void svr_getopts(int argc, char ** argv) {
 	char* recv_window_arg = NULL;
 	char* keepalive_arg = NULL;
 	char* idle_timeout_arg = NULL;
+	char* maxauthtries_arg = NULL;
 	char* keyfile = NULL;
 	char c;
 
@@ -130,6 +133,7 @@ void svr_getopts(int argc, char ** argv) {
 	svr_opts.noauthpass = 0;
 	svr_opts.norootpass = 0;
 	svr_opts.allowblankpass = 0;
+	svr_opts.maxauthtries = DEFAULT_AUTH_TRIES;
 	svr_opts.inetdmode = 0;
 	svr_opts.portcount = 0;
 	svr_opts.hostkey = NULL;
@@ -234,6 +238,9 @@ void svr_getopts(int argc, char ** argv) {
 				case 'I':
 					next = &idle_timeout_arg;
 					break;
+				case 'T':
+					next = &maxauthtries_arg;
+					break;
 #if defined(ENABLE_SVR_PASSWORD_AUTH) || defined(ENABLE_SVR_PAM_AUTH)
 				case 's':
 					svr_opts.noauthpass = 1;
@@ -330,6 +337,16 @@ void svr_getopts(int argc, char ** argv) {
 			dropbear_exit("Bad recv window '%s'", recv_window_arg);
 		}
 	}
+
+	if (maxauthtries_arg) {
+		unsigned int val = 0;
+		if (m_str_to_uint(maxauthtries_arg, &val) == DROPBEAR_FAILURE ||
+			val == 0 || val > MAX_AUTH_TRIES) {
+			dropbear_exit("Bad maxauthtries '%s'", maxauthtries_arg);
+		}
+		svr_opts.maxauthtries = val;
+	}
+
 	
 	if (keepalive_arg) {
 		unsigned int val;
-- 
2.7.4