Support ident authentication on local (Unix) socket connections, if the

system supports SO_PEERCRED requests for Unix sockets.  This is an
amalgamation of patches submitted by Helge Bahmann and Oliver Elphick,
with some editorializing by yours truly.

configure.in

@@ -801,6 +801,19 @@ AC_CHECK_FUNCS([fcvt getopt_long memmove pstat setproctitle setsid sigprocmask s
 dnl Check whether <unistd.h> declares fdatasync().
 AC_EGREP_HEADER(fdatasync, unistd.h, AC_DEFINE(HAVE_FDATASYNC_DECL))
 
+AC_MSG_CHECKING([for SO_PEERCRED])
+AC_EGREP_CPP(HAVE_SO_PEERCRED,
+#include <sys/socket.h>
+#ifdef SO_PEERCRED
+HAVE_SO_PEERCRED
+#endif
+],
+[
+  AC_MSG_RESULT(yes)
+  AC_DEFINE(HAVE_SO_PEERCRED)
+],
+[AC_MSG_RESULT(no)])
+
 AC_CACHE_CHECK([for PS_STRINGS], [pgac_cv_var_PS_STRINGS],
 [AC_TRY_LINK(
 [#include <machine/vmparam.h>

doc/src/sgml/client-auth.sgml

-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/client-auth.sgml,v 1.14 2001/08/01 00:48:52 momjian Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/client-auth.sgml,v 1.15 2001/08/01 23:25:39 tgl Exp $ -->
 
 <chapter id="client-authentication">
  <title>Client Authentication</title>
@@ -238,12 +238,26 @@ hostssl <replaceable>database</replaceable> <replaceable>IP-address</replaceable
         <term>ident</term>
         <listitem>
 	 <para>
-          The ident server on the client host is asked for the identity
-          of the connecting user. <productname>Postgres</productname>
-          then verifies whether the so identified operating system user
-          is allowed to connect as the database user that is requested.
-	  This is only available for TCP/IP connections.  It can be used
-	  on the local machine by specifying the localhost address 127.0.0.1.
+	  The identity of the user as determined on login to the
+	  operating system is used by <productname>Postgres</productname>
+	  to determine whether the user
+          is allowed to connect as the requested database user.
+	  For TCP/IP connections the user's identity is determined by
+	  contacting the <firstterm>ident</firstterm> server on the client
+	  host.  (Note that this is only as reliable as the remote ident
+	  server; ident authentication should never be used for remote hosts
+	  whose administrators are not trustworthy.)
+	  On operating systems
+	  supporting SO_PEERCRED requests for Unix domain sockets,
+	  ident authentication is possible for local connections;
+	  the system is then asked for the connecting user's identity.
+	 </para>
+         <para>
+	  On systems without SO_PEERCRED requests, ident authentication
+	  is only available for TCP/IP connections.  As a workaround,
+	  it is possible to
+	  specify the localhost address 127.0.0.1 and make connections
+	  to this address.
 	 </para>
          <para>
           The <replaceable>authentication option</replaceable> following
@@ -283,7 +297,8 @@ hostssl <replaceable>database</replaceable> <replaceable>IP-address</replaceable
    The <filename>pg_hba.conf</filename> file is loaded only on startup
    and when the <application>postmaster</> receives a SIGHUP signal. If
    you edit the file on an active system, you will need to issue a
-   SIGHUP to the <application>postmaster</> using <application>kill</>.
+   SIGHUP to the <application>postmaster</> using <application>kill</>
+   to make it re-read the file.
   </para>
 
   <para>
@@ -563,11 +578,19 @@ host         all        192.168.0.0    255.255.0.0        ident     omicron
     You must trust the machine running the ident server.
    </para>
 
+   <para>
+    On systems supporting SO_PEERCRED requests for Unix-domain sockets,
+    ident authentication can also be applied to local connections.  In this
+    case, no security risk is added by using ident authentication; indeed
+    it is a preferable choice for such a system.
+   </para>
+
    <para>
     When using ident-based authentication, after having determined the
-    operating system user that initiated the connection,
-    <productname>Postgres</productname> determines as what database
-    system user he may connect. This is controlled by the ident map
+    name of the operating system user that initiated the connection,
+    <productname>Postgres</productname> checks whether that user is allowed
+    to connect as the database user he is requesting to connect as.
+    This is controlled by the ident map
     argument that follows the <literal>ident</> keyword in the
     <filename>pg_hba.conf</filename> file. The simplest ident map is
     <literal>sameuser</literal>, which allows any operating system
@@ -588,8 +611,9 @@ host         all        192.168.0.0    255.255.0.0        ident     omicron
     The other two fields specify which operating system user is
     allowed to connect as which database user. The same
     <replaceable>map-name</> can be used repeatedly to specify more
-    user-mappings. There is also no restriction regarding how many
-    database users a given operating system may correspond to and vice
+    user-mappings within a single map. There is no restriction regarding
+    how many 
+    database users a given operating system user may correspond to and vice
     versa.
    </para>
 
@@ -669,6 +693,12 @@ FATAL 1:  Database "testdb" does not exist in the system catalog.
     if you don't specify a database name, it defaults to the database
     user name, which may or may not be the right thing.
    </para>
+
+   <para>
+    Note that the postmaster's stderr log may contain more information
+    about an authentication failure than is reported to the client.
+    If you are confused about the reason for a failure, check the log.
+   </para>
   </sect1>
 
  </chapter>

src/backend/libpq/auth.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/libpq/auth.c,v 1.54 2001/07/21 00:29:56 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/libpq/auth.c,v 1.55 2001/08/01 23:25:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -494,8 +494,7 @@ ClientAuthentication(Port *port)
 			break;
 
 		case uaIdent:
-			status = authident(&port->raddr.in, &port->laddr.in,
-							   port->user, port->auth_arg);
+			status = authident(port);
 			break;
 
 		case uaPassword:
@@ -654,8 +653,7 @@ map_old_to_new(Port *port, UserAuth old, int status)
 			break;
 
 		case uaIdent:
-			status = authident(&port->raddr.in, &port->laddr.in,
-							   port->user, port->auth_arg);
+			status = authident(port);
 			break;
 
 		case uaPassword:

src/backend/libpq/hba.c

@@ -5,7 +5,7 @@
  *	  wherein you authenticate a user by seeing what IP address the system
  *	  says he comes from and possibly using ident).
  *
- *	$Id: hba.c,v 1.57 2001/07/31 22:55:45 tgl Exp $
+ *	$Id: hba.c,v 1.58 2001/08/01 23:25:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -286,12 +286,25 @@ parse_hba(List *line, hbaPort *port, bool *found_p, bool *error_p)
 
 		/*
 		 * Disallow auth methods that need AF_INET sockets to work.
+		 * Allow "ident" if we can get the identity of the connection
+		 * peer on Unix domain sockets from the OS.
 		 */
-		if (!*error_p &&
-			(port->auth_method == uaIdent ||
-			 port->auth_method == uaKrb4 ||
-			 port->auth_method == uaKrb5))
+		if (port->auth_method == uaKrb4 ||
+			port->auth_method == uaKrb5)
 			goto hba_syntax;
+#ifndef HAVE_SO_PEERCRED
+		if (port->auth_method == uaIdent)
+		{
+			/* Give a special error message for this case... */
+			snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+					 "parse_hba: \"ident\" auth is not supported on local connections on this platform\n");
+			fputs(PQerrormsg, stderr);
+			pqdebug("%s", PQerrormsg);
+
+			*error_p = true;
+			return;
+		}
+#endif
 
 		/*
 		 * If this record doesn't match the parameters of the connection
@@ -732,8 +745,8 @@ interpret_ident_response(char *ident_response,
  *
  *  But iff we're unable to get the information from ident, return false.
  */
-static int
-ident(const struct in_addr remote_ip_addr,
+static bool
+ident_inet(const struct in_addr remote_ip_addr,
 		   const struct in_addr local_ip_addr,
 		   const ushort remote_port,
 		   const ushort local_port,
@@ -848,28 +861,103 @@ ident(const struct in_addr remote_ip_addr,
 	return ident_return;
 }
 
+#ifdef HAVE_SO_PEERCRED
+/*
+ *  Ask kernel about the credentials of the connecting process and
+ *  determine the symbolic name of the corresponding user.
+ *
+ *  Returns either true and the username put into "ident_user",
+ *  or false if we were unable to determine the username.
+ */
+static bool
+ident_unix(int sock, char *ident_user)
+{
+	struct ucred	peercred;
+	socklen_t		so_len;
+	struct passwd *pass;
+
+#ifdef SO_PASSCRED
+	int passcred = -1;
+
+	so_len = sizeof(passcred);
+	if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &passcred, so_len) != 0)
+	{
+		/* We could not set the socket to pass credentials */
+		snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+				 "Could not set the UNIX socket to pass credentials: %s\n",
+				 strerror(errno));
+		fputs(PQerrormsg, stderr);
+		pqdebug("%s", PQerrormsg);
+		return false;
+	}
+#endif /* SO_PASSCRED */
+
+	errno = 0;
+	so_len = sizeof(peercred);
+	if (getsockopt(sock, SOL_SOCKET, SO_PEERCRED, &peercred, &so_len) != 0 ||
+		so_len != sizeof(peercred))
+	{
+		/* We didn't get a valid credentials struct. */
+		snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+				 "Could not get valid credentials from the UNIX socket: %s\n",
+				 strerror(errno));
+		fputs(PQerrormsg, stderr);
+		pqdebug("%s", PQerrormsg);
+		return false;
+	}
+
+	/* Convert UID to user login name */
+	pass = getpwuid(peercred.uid);
+
+	if (pass == NULL)
+	{
+		/* Error - no username with the given uid */
+		snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+				 "There is no entry in /etc/passwd with the socket's uid\n");
+		fputs(PQerrormsg, stderr);
+		pqdebug("%s", PQerrormsg);
+		return false;
+	}
+
+	StrNCpy(ident_user, pass->pw_name, IDENT_USERNAME_MAX);
+
+	return true;
+}
+#endif
 
 /*
- *  Talk to the ident server on the remote host and find out who owns the
- *  connection described by "port".  Then look in the usermap file under
- *  the usermap *auth_arg and see if that user is equivalent to
- *  Postgres user *user.
+ *  Determine the username of the initiator of the connection described
+ *  by "port".  Then look in the usermap file under the usermap
+ *  port->auth_arg and see if that user is equivalent to Postgres user
+ *  port->user.
  *
- *  Return STATUS_OK if yes.
+ *  Return STATUS_OK if yes, STATUS_ERROR if no match (or couldn't get info).
  */
 int
-authident(struct sockaddr_in *raddr, struct sockaddr_in *laddr,
-		  const char *pg_user, const char *auth_arg)
+authident(hbaPort *port)
 {
-	/* We were unable to get ident to give us a username */
 	char		ident_user[IDENT_USERNAME_MAX + 1];
 
-	/* The username returned by ident */
-	if (!ident(raddr->sin_addr, laddr->sin_addr,
-		  raddr->sin_port, laddr->sin_port, ident_user))
+	switch (port->raddr.sa.sa_family)
+	{
+		case AF_INET:
+			if (!ident_inet(port->raddr.in.sin_addr,
+							port->laddr.in.sin_addr,
+							port->raddr.in.sin_port,
+							port->laddr.in.sin_port, ident_user))
 				return STATUS_ERROR;
+			break;
+#ifdef HAVE_SO_PEERCRED
+		case AF_UNIX:
+			if (!ident_unix(port->sock, ident_user))
+				return STATUS_ERROR;
+			break;
+#endif
+		default:
+			return STATUS_ERROR;
+	}
 
-	if (check_ident_usermap(auth_arg, pg_user, ident_user))
+	if (check_ident_usermap(port->auth_arg, port->user, ident_user))
 		return STATUS_OK;
 	else
 		return STATUS_ERROR;

src/backend/libpq/pg_hba.conf.sample

@@ -126,28 +126,31 @@
 #		usernames stored in secondary password files but not
 #		secondary passwords.
 # 
-#   ident:	Authentication is done by the ident server on the local
-#		(127.0.0.1) or remote host. AUTH_ARGUMENT is required and
-#		maps names found in the $PGDATA/pg_ident.conf file. The 
-#		connection is accepted if the file contains an entry for
-#		this map name with the ident-supplied username and the 
-#		requested PostgreSQL username. The special map name 
-#		"sameuser" indicates an implied map (not in pg_ident.conf)
-#		that maps each ident username to the identical PostgreSQL 
-#		username.
-# 
-#   krb4:	Kerberos V4 authentication is used.
-# 
-#   krb5:	Kerberos V5 authentication is used.
+#   ident:	For TCP/IP connections, authentication is done by contacting
+#		the ident server on the client host.  (CAUTION: this is only
+#		as secure as the client machine!)  On machines that support
+#		SO_PEERCRED socket requests, this method also works for
+#		local Unix-domain connections.  AUTH_ARGUMENT is required:
+#		it determines how to map remote user names to Postgres user
+#		names.  The AUTH_ARGUMENT is a map name found in the
+#		$PGDATA/pg_ident.conf file. The connection is accepted if
+#		that file contains an entry for this map name with the
+#		ident-supplied username and the requested Postgres username.
+#		The special map name "sameuser" indicates an implied map
+#		(not in pg_ident.conf) that maps each ident username to the
+#		identical PostgreSQL username.
+# 
+#   krb4:	Kerberos V4 authentication is used.  Allowed only for
+#		TCP/IP connections, not for local UNIX-domain sockets.
+# 
+#   krb5:	Kerberos V5 authentication is used.  Allowed only for
+#		TCP/IP connections, not for local UNIX-domain sockets.
 # 
 #   reject: 	Reject the connection. This is used to reject certain hosts
 #		that are part of a network specified later in the file.
 #		To be effective, "reject" must appear before the later
 #		entries.
 # 
-# Local UNIX-domain socket connections support only the AUTH_TYPEs of
-# "trust", "password", "crypt", and "reject".
-# 
 # 
 # 
 # Examples

src/include/config.h.in

@@ -8,7 +8,7 @@
  * or in config.h afterwards.  Of course, if you edit config.h, then your
  * changes will be overwritten the next time you run configure.
  *
- * $Id: config.h.in,v 1.168 2001/07/16 05:07:00 tgl Exp $
+ * $Id: config.h.in,v 1.169 2001/08/01 23:25:39 tgl Exp $
  */
 
 #ifndef CONFIG_H
@@ -685,6 +685,9 @@ extern int fdatasync(int fildes);
 /* Define if you have on_exit() */
 #undef HAVE_ON_EXIT
 
+/* Define if you have SO_PEERCRED */
+#undef HAVE_SO_PEERCRED
+
 /*
  *------------------------------------------------------------------------
  * Part 4: pull in system-specific declarations.

src/include/libpq/hba.h

@@ -4,7 +4,7 @@
  *	  Interface to hba.c
  *
  *
- * $Id: hba.h,v 1.21 2001/07/31 22:55:45 tgl Exp $
+ * $Id: hba.h,v 1.22 2001/08/01 23:25:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,8 +41,7 @@ typedef enum UserAuth
 typedef struct Port hbaPort;
 
 extern int hba_getauthmethod(hbaPort *port);
-extern int authident(struct sockaddr_in *raddr, struct sockaddr_in *laddr,
-					 const char *postgres_username, const char *auth_arg);
+extern int authident(hbaPort *port);
 extern void load_hba_and_ident(void);
 
 #endif