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, 28 insertions, 0 deletions

diff --git a/src/include/fe_utils/connect.h b/src/include/fe_utils/connect.h
new file mode 100644
index 00000000000..fa293d2458d
--- /dev/null
+++ b/src/include/fe_utils/connect.h
@@ -0,0 +1,28 @@
+/*-------------------------------------------------------------------------
+ *
+ * Interfaces in support of FE/BE connections.
+ *
+ *
+ * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/fe_utils/connect.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef CONNECT_H
+#define CONNECT_H
+
+/*
+ * This SQL statement installs an always-secure search path, so malicious
+ * users can't take control.  CREATE of an unqualified name will fail, because
+ * this selects no creation schema.  This does not demote pg_temp, so it is
+ * suitable where we control the entire FE/BE connection but not suitable in
+ * SECURITY DEFINER functions.  This is portable to PostgreSQL 7.3, which
+ * introduced schemas.  When connected to an older version from code that
+ * might work with the old server, skip this.
+ */
+#define ALWAYS_SECURE_SEARCH_PATH_SQL \
+	"SELECT pg_catalog.set_config('search_path', '', false)"
+
+#endif							/* CONNECT_H */