Fix has_column_privilege function corner case

According to the comments, when an invalid or dropped column oid is passed
to has_column_privilege(), the intention has always been to return NULL.
However, when the caller had table level privilege the invalid/missing
column was never discovered, because table permissions were checked first.

Fix that by introducing extended versions of pg_attribute_acl(check|mask)
and pg_class_acl(check|mask) which take a new argument, is_missing. When
is_missing is NULL, the old behavior is preserved. But when is_missing is
passed by the caller, no ERROR is thrown for dropped or missing
columns/relations, and is_missing is flipped to true. This in turn allows
has_column_privilege to check for column privileges first, providing the
desired semantics.

Not backpatched since it is a user visible behavioral change with no previous
complaints, and the fix is a bit on the invasive side.

Author: Joe Conway
Reviewed-By: Tom Lane
Reported by: Ian Barwick
Discussion: https://postgr.es/m/flat/9b5f4311-157b-4164-7fe7-077b4fe8ed84%40joeconway.com

2 files changed, 15 insertions, 1 deletions

diff --git a/src/test/regress/expected/privileges.out b/src/test/regress/expected/privileges.out
index 4903371991f..89f3d5da46e 100644
--- a/src/test/regress/expected/privileges.out
+++ b/src/test/regress/expected/privileges.out
@@ -1362,7 +1362,13 @@ select has_column_privilege('mytable','........pg.dropped.2........','select');
 select has_column_privilege('mytable',2::int2,'select');
  has_column_privilege 
 ----------------------
- t
+ 
+(1 row)
+
+select has_column_privilege('mytable',99::int2,'select');
+ has_column_privilege 
+----------------------
+ 
 (1 row)
 
 revoke select on table mytable from regress_priv_user3;
@@ -1372,6 +1378,12 @@ select has_column_privilege('mytable',2::int2,'select');
  
 (1 row)
 
+select has_column_privilege('mytable',99::int2,'select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
 drop table mytable;
 -- Grant options
 SET SESSION AUTHORIZATION regress_priv_user1;
diff --git a/src/test/regress/sql/privileges.sql b/src/test/regress/sql/privileges.sql
index 8dcd2199e0d..22337310af3 100644
--- a/src/test/regress/sql/privileges.sql
+++ b/src/test/regress/sql/privileges.sql
@@ -836,8 +836,10 @@ alter table mytable drop column f2;
 select has_column_privilege('mytable','f2','select');
 select has_column_privilege('mytable','........pg.dropped.2........','select');
 select has_column_privilege('mytable',2::int2,'select');
+select has_column_privilege('mytable',99::int2,'select');
 revoke select on table mytable from regress_priv_user3;
 select has_column_privilege('mytable',2::int2,'select');
+select has_column_privilege('mytable',99::int2,'select');
 drop table mytable;
 
 -- Grant options