Empty search_path in Autovacuum and non-psql/pgbench clients.

This makes the client programs behave as documented regardless of the
connect-time search_path and regardless of user-created objects.  Today,
a malicious user with CREATE permission on a search_path schema can take
control of certain of these clients' queries and invoke arbitrary SQL
functions under the client identity, often a superuser.  This is
exploitable in the default configuration, where all users have CREATE
privilege on schema "public".

This changes behavior of user-defined code stored in the database, like
pg_index.indexprs and pg_extension_config_dump().  If they reach code
bearing unqualified names, "does not exist" or "no schema has been
selected to create in" errors might appear.  Users may fix such errors
by schema-qualifying affected names.  After upgrading, consider watching
server logs for these errors.

The --table arguments of src/bin/scripts clients have been lax; for
example, "vacuumdb -Zt pg_am\;CHECKPOINT" performed a checkpoint.  That
now fails, but for now, "vacuumdb -Zt 'pg_am(amname);CHECKPOINT'" still
performs a checkpoint.

Back-patch to 9.3 (all supported versions).

Reviewed by Tom Lane, though this fix strategy was not his first choice.
Reported by Arseniy Sharoglazov.

Security: CVE-2018-1058

1 files changed, 11 insertions, 0 deletions

diff --git a/src/bin/pg_dump/pg_backup_db.c b/src/bin/pg_dump/pg_backup_db.c
index fea10bce298..fa69e64bdbd 100644
--- a/src/bin/pg_dump/pg_backup_db.c
+++ b/src/bin/pg_dump/pg_backup_db.c
@@ -10,6 +10,7 @@
  *-------------------------------------------------------------------------
  */
 
+#include "fe_utils/connect.h"
 #include "pg_backup_db.h"
 #include "pg_backup_utils.h"
 #include "dumputils.h"
@@ -96,6 +97,11 @@ ReconnectToServer(ArchiveHandle *AH, const char *dbname, const char *username)
 	PQfinish(AH->connection);
 	AH->connection = newConn;
 
+	/* Start strict; later phases may override this. */
+	if (PQserverVersion(AH->connection) >= 70300)
+		PQclear(ExecuteSqlQueryForSingleRow((Archive *) AH,
+											ALWAYS_SECURE_SEARCH_PATH_SQL));
+
 	return 1;
 }
 
@@ -304,6 +310,11 @@ ConnectDatabase(Archive *AHX,
 					  PQdb(AH->connection) ? PQdb(AH->connection) : "",
 					  PQerrorMessage(AH->connection));
 
+	/* Start strict; later phases may override this. */
+	if (PQserverVersion(AH->connection) >= 70300)
+		PQclear(ExecuteSqlQueryForSingleRow((Archive *) AH,
+											ALWAYS_SECURE_SEARCH_PATH_SQL));
+
 	/*
 	 * We want to remember connection's actual password, whether or not we got
 	 * it by prompting.  So we don't just store the password variable.