[RFC PATCH 3/4] pam-ssh-agent: Add connecting to the SSH agent

[Domenico Andreoli]

The module now connects to the agent and fetches the identities therein
stored, if any.

Tests verify the behavior in case of missing SSH_AUTH_SOCK, communication
issues and empty ssh-agent.

Signed-off-by: Domenico Andreoli <domenico.andreoli at linux.com>

---
 pam-ssh-agent.c          |   31 +++++++++++++++++++++++++++++++
 regress/pam-ssh-agent.sh |   24 ++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

Index: b/pam-ssh-agent.c
===================================================================
--- a/pam-ssh-agent.c
+++ b/pam-ssh-agent.c
@@ -38,6 +38,7 @@
 #include "authfile.h"
 #include "authfd.h"
 #include "ssherr.h"
+#include "ssh.h"
 
 static int pam_debug;
 static const char *auth_file;
@@ -97,7 +98,9 @@ ssh_read_identitylist(const char *filena
 int
 pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc, const char **argv)
 {
+	struct ssh_identitylist *agent_ids = NULL;
 	struct ssh_identitylist *auth_ids = NULL;
+	int agent_fd = -1;
 	int ret;
 
 	openlog("pam_ssh_agent_auth", 0, LOG_AUTHPRIV);
@@ -108,10 +111,13 @@ pam_sm_authenticate(pam_handle_t *pamh,
 	}
 
 	if (pam_debug) {
+		const char *auth_socket = getenv(SSH_AUTHSOCKET_ENV_NAME);
 		const char *user = "(unknown)";
 		pam_get_user(pamh, &user, NULL);
 		syslog(LOG_DEBUG, "USER: %s", user);
 		syslog(LOG_DEBUG, "FILE: %s", auth_file ? auth_file : "(null)");
+		auth_socket = auth_socket ? auth_socket : "(null)";
+		syslog(LOG_DEBUG, "%s: %s", SSH_AUTHSOCKET_ENV_NAME, auth_socket);
 	}
 
 	if (auth_file == NULL) {
@@ -134,9 +140,34 @@ pam_sm_authenticate(pam_handle_t *pamh,
 			syslog(LOG_DEBUG, "  %d) %s", i, auth_ids->comments[i]);
 	}
 
+	ret = ssh_get_authentication_socket(&agent_fd);
+	if (ret) {
+		syslog(LOG_NOTICE, "agent error: %s", ssh_err(ret));
+		ret = PAM_AUTH_ERR;
+		goto out;
+	}
+
+	ret = ssh_fetch_identitylist(agent_fd, &agent_ids);
+	if (ret) {
+		syslog(LOG_NOTICE, "agent error: %s", ssh_err(ret));
+		ret = PAM_AUTH_ERR;
+		goto out;
+	}
+
+	if (pam_debug) {
+		unsigned i;
+		syslog(LOG_DEBUG, "agent has %u key(s):", (unsigned) agent_ids->nkeys);
+		for (i=0; i!=agent_ids->nkeys; i++)
+			syslog(LOG_DEBUG, "  %d) %s", i, agent_ids->comments[i]);
+	}
+
 	ret = PAM_SUCCESS;
 
 out:
+	if (agent_fd != -1)
+		ssh_close_authentication_socket(agent_fd);
+	if (agent_ids != NULL)
+		ssh_free_identitylist(agent_ids);
 	if (auth_ids != NULL)
 		ssh_free_identitylist(auth_ids);
 	if (pam_debug)
Index: b/regress/pam-ssh-agent.sh
===================================================================
--- a/regress/pam-ssh-agent.sh
+++ b/regress/pam-ssh-agent.sh
@@ -14,6 +14,7 @@ export PAM_WRAPPER_SERVICE_DIR=$OBJ/pam-
 
 PAM_SUCCESS=0
 PAM_SERVICE_ERR=3
+PAM_AUTH_ERR=7
 PAM_AUTHINFO_UNAVAIL=9
 
 . $OBJ/keytype_gen.sh
@@ -52,8 +53,31 @@ expect=$PAM_AUTHINFO_UNAVAIL  pam_agent_
 trace "with empty auth file"
 expect=$PAM_AUTHINFO_UNAVAIL  pam_agent_test file=/dev/null
 
+trace "start agent"
+eval `${SSHAGENT} ${EXTRA_AGENT_ARGS} -s` > /dev/null
+r=$?
+if [ $r -ne 0 ]; then
+	fatal "could not start ssh-agent: exit code $r"
+fi
+
+trace "load key into the agent"
+${SSHADD} -q $OBJ/key.$first_kt
+r=$?
+if [ $r -ne 0 ]; then
+	fatal "could not add the key: exit code $r"
+fi
+
 trace "authenticate agent (debug)"
 expect=$PAM_SUCCESS           pam_agent_test file=$AUTH_FILE debug
 
 trace "authenticate agent (non-debug)"
 expect=$PAM_SUCCESS           pam_agent_test file=$AUTH_FILE
+
+trace "kill agent"
+${SSHAGENT} -k > /dev/null
+
+trace "agent is gone (debug)"
+expect=$PAM_AUTH_ERR          pam_agent_test file=$AUTH_FILE debug
+
+trace "agent is gone (non-debug)"
+expect=$PAM_AUTH_ERR          pam_agent_test file=$AUTH_FILE