Handle PAM_MAXTRIES from modules.

bz#2249: handle the case where PAM returns PAM_MAXTRIES by ceasing to offer
password and keyboard-interative authentication methods.  Should prevent
"sshd ignoring max retries" warnings in the log.  ok djm@

It probably won't trigger with keyboard-interactive in the default
configuration because the retry counter is stored in module-private
storage which goes away with the sshd PAM process (see bz#688).  On the
other hand, those cases probably won't log a warning either.

auth-pam.c

@@ -229,6 +229,7 @@ static int sshpam_authenticated = 0;
 static int sshpam_session_open = 0;
 static int sshpam_cred_established = 0;
 static int sshpam_account_status = -1;
+static int sshpam_maxtries_reached = 0;
 static char **sshpam_env = NULL;
 static Authctxt *sshpam_authctxt = NULL;
 static const char *sshpam_password = NULL;
@@ -450,6 +451,8 @@ sshpam_thread(void *ctxtp)
 	if (sshpam_err != PAM_SUCCESS)
 		goto auth_fail;
 	sshpam_err = pam_authenticate(sshpam_handle, flags);
+	if (sshpam_err == PAM_MAXTRIES)
+		sshpam_set_maxtries_reached(1);
 	if (sshpam_err != PAM_SUCCESS)
 		goto auth_fail;
 
@@ -501,6 +504,8 @@ sshpam_thread(void *ctxtp)
 	/* XXX - can't do much about an error here */
 	if (sshpam_err == PAM_ACCT_EXPIRED)
 		ssh_msg_send(ctxt->pam_csock, PAM_ACCT_EXPIRED, &buffer);
+	else if (sshpam_maxtries_reached)
+		ssh_msg_send(ctxt->pam_csock, PAM_MAXTRIES, &buffer);
 	else
 		ssh_msg_send(ctxt->pam_csock, PAM_AUTH_ERR, &buffer);
 	buffer_free(&buffer);
@@ -741,7 +746,11 @@ sshpam_query(void *ctx, char **name, char **info,
 			free(msg);
 			break;
 		case PAM_ACCT_EXPIRED:
-			sshpam_account_status = 0;
+		case PAM_MAXTRIES:
+			if (type == PAM_ACCT_EXPIRED)
+				sshpam_account_status = 0;
+			if (type == PAM_MAXTRIES)
+				sshpam_set_maxtries_reached(1);
 			/* FALLTHROUGH */
 		case PAM_AUTH_ERR:
 			debug3("PAM: %s", pam_strerror(sshpam_handle, type));
@@ -1218,6 +1227,8 @@ sshpam_auth_passwd(Authctxt *authctxt, const char *password)
 	sshpam_err = pam_authenticate(sshpam_handle, flags);
 	sshpam_password = NULL;
 	free(fake);
+	if (sshpam_err == PAM_MAXTRIES)
+		sshpam_set_maxtries_reached(1);
 	if (sshpam_err == PAM_SUCCESS && authctxt->valid) {
 		debug("PAM: password authentication accepted for %.100s",
 		    authctxt->user);
@@ -1229,4 +1240,21 @@ sshpam_auth_passwd(Authctxt *authctxt, const char *password)
 		return 0;
 	}
 }
+
+int
+sshpam_get_maxtries_reached(void)
+{
+	return sshpam_maxtries_reached;
+}
+
+void
+sshpam_set_maxtries_reached(int reached)
+{
+	if (reached == 0 || sshpam_maxtries_reached)
+		return;
+	sshpam_maxtries_reached = 1;
+	options.password_authentication = 0;
+	options.kbd_interactive_authentication = 0;
+	options.challenge_response_authentication = 0;
+}
 #endif /* USE_PAM */

auth-pam.h

@@ -45,6 +45,8 @@ void free_pam_environment(char **);
 void sshpam_thread_cleanup(void);
 void sshpam_cleanup(void);
 int sshpam_auth_passwd(Authctxt *, const char *);
+int sshpam_get_maxtries_reached(void);
+void sshpam_set_maxtries_reached(int);
 int is_pam_session_open(void);
 
 #endif /* USE_PAM */

monitor.c

@@ -75,6 +75,7 @@
 #include "cipher.h"
 #include "kex.h"
 #include "dh.h"
+#include "auth-pam.h"
 #ifdef TARGET_OS_MAC	/* XXX Broken krb5 headers on Mac */
 #undef TARGET_OS_MAC
 #include "zlib.h"
@@ -920,6 +921,9 @@ mm_answer_authpassword(int sock, Buffer *m)
 
 	buffer_clear(m);
 	buffer_put_int(m, authenticated);
+#ifdef USE_PAM
+	buffer_put_int(m, sshpam_get_maxtries_reached());
+#endif
 
 	debug3("%s: sending result %d", __func__, authenticated);
 	mm_request_send(sock, MONITOR_ANS_AUTHPASSWORD, m);
@@ -1119,6 +1123,7 @@ mm_answer_pam_query(int sock, Buffer *m)
 	free(name);
 	buffer_put_cstring(m, info);
 	free(info);
+	buffer_put_int(m, sshpam_get_maxtries_reached());
 	buffer_put_int(m, num);
 	for (i = 0; i < num; ++i) {
 		buffer_put_cstring(m, prompts[i]);

monitor_wrap.c

@@ -60,6 +60,7 @@
 #include "packet.h"
 #include "mac.h"
 #include "log.h"
+#include "auth-pam.h"
 #ifdef TARGET_OS_MAC    /* XXX Broken krb5 headers on Mac */
 #undef TARGET_OS_MAC
 #include "zlib.h"
@@ -362,6 +363,9 @@ mm_auth_password(Authctxt *authctxt, char *password)
 	mm_request_receive_expect(pmonitor->m_recvfd, MONITOR_ANS_AUTHPASSWORD, &m);
 
 	authenticated = buffer_get_int(&m);
+#ifdef USE_PAM
+	sshpam_set_maxtries_reached(buffer_get_int(&m));
+#endif
 
 	buffer_free(&m);
 
@@ -644,6 +648,7 @@ mm_sshpam_query(void *ctx, char **name, char **info,
 	debug3("%s: pam_query returned %d", __func__, ret);
 	*name = buffer_get_string(&m, NULL);
 	*info = buffer_get_string(&m, NULL);
+	sshpam_set_maxtries_reached(buffer_get_int(&m));
 	*num = buffer_get_int(&m);
 	if (*num > PAM_MAX_NUM_MSG)
 		fatal("%s: recieved %u PAM messages, expected <= %u",