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, 14 insertions, 0 deletions

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 579b8ae1937..4e15bad87fb 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -574,6 +574,12 @@ AutoVacLauncherMain(int argc, char *argv[])
 	PG_SETMASK(&UnBlockSig);
 
 	/*
+	 * Set always-secure search path.  Launcher doesn't connect to a database,
+	 * so this has no effect.
+	 */
+	SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
 	 * Force zero_damaged_pages OFF in the autovac process, even if it is set
 	 * in postgresql.conf.  We don't really want such a dangerous option being
 	 * applied non-interactively.
@@ -1584,6 +1590,14 @@ AutoVacWorkerMain(int argc, char *argv[])
 	PG_SETMASK(&UnBlockSig);
 
 	/*
+	 * Set always-secure search path, so malicious users can't redirect user
+	 * code (e.g. pg_index.indexprs).  (That code runs in a
+	 * SECURITY_RESTRICTED_OPERATION sandbox, so malicious users could not
+	 * take control of the entire autovacuum worker in any case.)
+	 */
+	SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
 	 * Force zero_damaged_pages OFF in the autovac process, even if it is set
 	 * in postgresql.conf.  We don't really want such a dangerous option being
 	 * applied non-interactively.