From 94bc1e7ffba3cbdea8c7dcdab8376bf29283128f Mon Sep 17 00:00:00 2001
From: Damien Miller <djm@mindrot.org>
Date: Fri, 28 Jul 2017 14:50:59 +1000
Subject: [PATCH] Expose list of completed auth methods to PAM

bz#2408; ok dtucker@
---
 auth-pam.c | 26 ++++++++++++++++++++++++++
 session.c  | 26 ++++++++++++++++++++------
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/auth-pam.c b/auth-pam.c
index 9574d9ac7..de29c04c9 100644
--- a/auth-pam.c
+++ b/auth-pam.c
@@ -926,6 +926,27 @@ finish_pam(void)
 	sshpam_cleanup();
 }
 
+static void
+expose_authinfo(const char *caller)
+{
+	char *auth_info;
+
+	/*
+	 * Expose authentication information to PAM.
+	 * The enviornment variable is versioned. Please increment the
+	 * version suffix if the format of session_info changes.
+	 */
+	if (sshpam_authctxt->session_info == NULL)
+		auth_info = xstrdup("");
+	else if ((auth_info = sshbuf_dup_string(
+	    sshpam_authctxt->session_info)) == NULL)
+		fatal("%s: sshbuf_dup_string failed", __func__);
+
+	debug2("%s: auth information in SSH_AUTH_INFO_0", caller);
+	do_pam_putenv("SSH_AUTH_INFO_0", auth_info);
+	free(auth_info);
+}
+
 u_int
 do_pam_account(void)
 {
@@ -933,6 +954,8 @@ do_pam_account(void)
 	if (sshpam_account_status != -1)
 		return (sshpam_account_status);
 
+	expose_authinfo(__func__);
+
 	sshpam_err = pam_acct_mgmt(sshpam_handle, 0);
 	debug3("PAM: %s pam_acct_mgmt = %d (%s)", __func__, sshpam_err,
 	    pam_strerror(sshpam_handle, sshpam_err));
@@ -1057,6 +1080,9 @@ void
 do_pam_session(void)
 {
 	debug3("PAM: opening session");
+
+	expose_authinfo(__func__);
+
 	sshpam_err = pam_set_item(sshpam_handle, PAM_CONV,
 	    (const void *)&store_conv);
 	if (sshpam_err != PAM_SUCCESS)
diff --git a/session.c b/session.c
index a2588e74b..698eaa879 100644
--- a/session.c
+++ b/session.c
@@ -984,8 +984,9 @@ read_etc_default_login(char ***env, u_int *envsize, uid_t uid)
 }
 #endif /* HAVE_ETC_DEFAULT_LOGIN */
 
-void
-copy_environment(char **source, char ***env, u_int *envsize)
+static void
+copy_environment_blacklist(char **source, char ***env, u_int *envsize,
+    const char *blacklist)
 {
 	char *var_name, *var_val;
 	int i;
@@ -1001,13 +1002,22 @@ copy_environment(char **source, char ***env, u_int *envsize)
 		}
 		*var_val++ = '\0';
 
-		debug3("Copy environment: %s=%s", var_name, var_val);
-		child_set_env(env, envsize, var_name, var_val);
+		if (blacklist == NULL ||
+		    match_pattern_list(var_name, blacklist, 0) != 1) {
+			debug3("Copy environment: %s=%s", var_name, var_val);
+			child_set_env(env, envsize, var_name, var_val);
+		}
 
 		free(var_name);
 	}
 }
 
+void
+copy_environment(char **source, char ***env, u_int *envsize)
+{
+	copy_environment_blacklist(source, env, envsize, NULL);
+}
+
 static char **
 do_setup_env(Session *s, const char *shell)
 {
@@ -1169,12 +1179,16 @@ do_setup_env(Session *s, const char *shell)
 	if (options.use_pam) {
 		char **p;
 
+		/*
+		 * Don't allow SSH_AUTH_INFO variables posted to PAM to leak
+		 * back into the environment.
+		 */
 		p = fetch_pam_child_environment();
-		copy_environment(p, &env, &envsize);
+		copy_environment_blacklist(p, &env, &envsize, "SSH_AUTH_INFO*");
 		free_pam_environment(p);
 
 		p = fetch_pam_environment();
-		copy_environment(p, &env, &envsize);
+		copy_environment_blacklist(p, &env, &envsize, "SSH_AUTH_INFO*");
 		free_pam_environment(p);
 	}
 #endif /* USE_PAM */