Set PAM_RHOST item for PAM authentication

The PAM_RHOST item is set to the remote IP address or host name and can
be used by PAM modules.  A pg_hba.conf option is provided to choose
between IP address and resolved host name.

From: Grzegorz Sampolski <grzsmp@gmail.com>
Reviewed-by: Haribabu Kommi <kommi.haribabu@gmail.com>

doc/src/sgml/client-auth.sgml

@@ -1617,10 +1617,11 @@ host ... ldap ldapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub"
     <literal>password</literal> except that it uses PAM (Pluggable
     Authentication Modules) as the authentication mechanism. The
     default PAM service name is <literal>postgresql</literal>.
-    PAM is used only to validate user name/password pairs.
-    Therefore the user must already exist in the database before PAM
-    can be used for authentication.  For more information about
-    PAM, please read the <ulink url="http://www.kernel.org/pub/linux/libs/pam/">
+    PAM is used only to validate user name/password pairs and optionally the
+    connected remote host name or IP address. Therefore the user must already
+    exist in the database before PAM can be used for authentication.  For more
+    information about PAM, please read the
+    <ulink url="http://www.kernel.org/pub/linux/libs/pam/">
     <productname>Linux-PAM</> Page</ulink>.
    </para>
 
@@ -1635,6 +1636,20 @@ host ... ldap ldapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub"
        </para>
       </listitem>
      </varlistentry>
+     <varlistentry>
+      <term><literal>pam_use_hostname</literal></term>
+      <listitem>
+       <para>
+        Determines whether the remote IP address or the host name is provided
+        to PAM modules through the <symbol>PAM_RHOST</symbol> item.  By
+        default, the IP address is used.  Set this option to 1 to use the
+        resolved host name instead.  Host name resolution can lead to login
+        delays.  (Most PAM configurations don't use this information, so it is
+        only necessary to consider this setting if a PAM configuration was
+        specifically created to make use of it.)
+       </para>
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
 

src/backend/libpq/auth.c

@@ -1739,6 +1739,18 @@ CheckPAMAuth(Port *port, char *user, char *password)
 {
 	int			retval;
 	pam_handle_t *pamh = NULL;
+	char		hostinfo[NI_MAXHOST];
+
+	retval = pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
+								hostinfo, sizeof(hostinfo), NULL, 0,
+								port->hba->pam_use_hostname ? 0 : NI_NUMERICHOST | NI_NUMERICSERV);
+	if (retval != 0)
+	{
+		ereport(WARNING,
+				(errmsg_internal("pg_getnameinfo_all() failed: %s",
+								 gai_strerror(retval))));
+		return STATUS_ERROR;
+	}
 
 	/*
 	 * We can't entirely rely on PAM to pass through appdata --- it appears
@@ -1784,6 +1796,17 @@ CheckPAMAuth(Port *port, char *user, char *password)
 		return STATUS_ERROR;
 	}
 
+	retval = pam_set_item(pamh, PAM_RHOST, hostinfo);
+
+	if (retval != PAM_SUCCESS)
+	{
+		ereport(LOG,
+				(errmsg("pam_set_item(PAM_RHOST) failed: %s",
+					pam_strerror(pamh, retval))));
+		pam_passwd = NULL;
+		return STATUS_ERROR;
+	}
+
 	retval = pam_set_item(pamh, PAM_CONV, &pam_passw_conv);
 
 	if (retval != PAM_SUCCESS)

src/backend/libpq/hba.c

@@ -1447,6 +1447,15 @@ parse_hba_auth_opt(char *name, char *val, HbaLine *hbaline, int line_num)
 		REQUIRE_AUTH_OPTION(uaPAM, "pamservice", "pam");
 		hbaline->pamservice = pstrdup(val);
 	}
+	else if (strcmp(name, "pam_use_hostname") == 0)
+	{
+		REQUIRE_AUTH_OPTION(uaPAM, "pam_use_hostname", "pam");
+		if (strcmp(val, "1") == 0)
+			hbaline->pam_use_hostname = true;
+		else
+			hbaline->pam_use_hostname = false;
+
+	}
 	else if (strcmp(name, "ldapurl") == 0)
 	{
 #ifdef LDAP_API_FEATURE_X_OPENLDAP

src/include/libpq/hba.h

@@ -64,6 +64,7 @@ typedef struct HbaLine
 
 	char	   *usermap;
 	char	   *pamservice;
+	bool		pam_use_hostname;
 	bool		ldaptls;
 	char	   *ldapserver;
 	int			ldapport;