Make REPLICATION privilege checks test current user not authenticated user.

The pg_start_backup() and pg_stop_backup() functions checked the privileges
of the initially-authenticated user rather than the current user, which is
wrong.  For example, a user-defined index function could successfully call
these functions when executed by ANALYZE within autovacuum.  This could
allow an attacker with valid but low-privilege database access to interfere
with creation of routine backups.  Reported and fixed by Noah Misch.

Security: CVE-2013-1901

src/backend/access/transam/xlog.c

@@ -8367,7 +8367,7 @@ do_pg_start_backup(const char *backupidstr, bool fast, TimeLineID *starttli_p,
 
 	backup_started_in_recovery = RecoveryInProgress();
 
-	if (!superuser() && !is_authenticated_user_replication_role())
+	if (!superuser() && !has_rolreplication(GetUserId()))
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 		   errmsg("must be superuser or replication role to run a backup")));
@@ -8705,7 +8705,7 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
 
 	backup_started_in_recovery = RecoveryInProgress();
 
-	if (!superuser() && !is_authenticated_user_replication_role())
+	if (!superuser() && !has_rolreplication(GetUserId()))
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 		 (errmsg("must be superuser or replication role to run a backup"))));

src/backend/utils/init/miscinit.c

@@ -390,15 +390,15 @@ SetUserIdAndContext(Oid userid, bool sec_def_context)
 
 
 /*
- * Check if the authenticated user is a replication role
+ * Check whether specified role has explicit REPLICATION privilege
  */
 bool
-is_authenticated_user_replication_role(void)
+has_rolreplication(Oid roleid)
 {
 	bool		result = false;
 	HeapTuple	utup;
 
-	utup = SearchSysCache1(AUTHOID, ObjectIdGetDatum(AuthenticatedUserId));
+	utup = SearchSysCache1(AUTHOID, ObjectIdGetDatum(roleid));
 	if (HeapTupleIsValid(utup))
 	{
 		result = ((Form_pg_authid) GETSTRUCT(utup))->rolreplication;

src/backend/utils/init/postinit.c

@@ -726,7 +726,7 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 	{
 		Assert(!bootstrap);
 
-		if (!superuser() && !is_authenticated_user_replication_role())
+		if (!superuser() && !has_rolreplication(GetUserId()))
 			ereport(FATAL,
 					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 					 errmsg("must be superuser or replication role to start walsender")));

src/include/miscadmin.h

@@ -439,7 +439,7 @@ extern void ValidatePgVersion(const char *path);
 extern void process_shared_preload_libraries(void);
 extern void process_local_preload_libraries(void);
 extern void pg_bindtextdomain(const char *domain);
-extern bool is_authenticated_user_replication_role(void);
+extern bool has_rolreplication(Oid roleid);
 
 /* in access/transam/xlog.c */
 extern bool BackupInProgress(void);