Fix corner-case failures in has_foo_privilege() family of functions.

The variants of these functions that take numeric inputs (OIDs or
column numbers) are supposed to return NULL rather than failing
on bad input; this rule reduces problems with snapshot skew when
queries apply the functions to all rows of a catalog.

has_column_privilege() had careless handling of the case where the
table OID didn't exist.  You might get something like this:
	select has_column_privilege(9999,'nosuchcol','select');
	ERROR:  column "nosuchcol" of relation "(null)" does not exist
or you might get a crash, depending on the platform's printf's response
to a null string pointer.

In addition, while applying the column-number variant to a dropped
column returned NULL as desired, applying the column-name variant
did not:
	select has_column_privilege('mytable','........pg.dropped.2........','select');
	ERROR:  column "........pg.dropped.2........" of relation "mytable" does not exist
It seems better to make this case return NULL as well.

Also, the OID-accepting variants of has_foreign_data_wrapper_privilege,
has_server_privilege, and has_tablespace_privilege didn't follow the
principle of returning NULL for nonexistent OIDs.  Superusers got TRUE,
everybody else got an error.

Per investigation of Jaime Casanova's report of a new crash in HEAD.
These behaviors have been like this for a long time, so back-patch to
all supported branches.

Patch by me; thanks to Stephen Frost for discussion and review

Discussion: https://postgr.es/m/CAJGNTeP=-6Gyqq5TN9OvYEydi7Fv1oGyYj650LGTnW44oAzYCg@mail.gmail.com

2 files changed, 74 insertions, 0 deletions

diff --git a/src/test/regress/expected/privileges.out b/src/test/regress/expected/privileges.out
index ac8968d24f5..aebc89c1b08 100644
--- a/src/test/regress/expected/privileges.out
+++ b/src/test/regress/expected/privileges.out
@@ -1132,6 +1132,63 @@ from (select oid from pg_class where relname = 'atest1') as t1;
  f
 (1 row)
 
+-- has_column_privilege function
+-- bad-input checks (as non-super-user)
+select has_column_privilege('pg_authid',NULL,'select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
+select has_column_privilege('pg_authid','nosuchcol','select');
+ERROR:  column "nosuchcol" of relation "pg_authid" does not exist
+select has_column_privilege(9999,'nosuchcol','select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
+select has_column_privilege(9999,99::int2,'select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
+select has_column_privilege('pg_authid',99::int2,'select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
+select has_column_privilege(9999,99::int2,'select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
+create temp table mytable(f1 int, f2 int, f3 int);
+alter table mytable drop column f2;
+select has_column_privilege('mytable','f2','select');
+ERROR:  column "f2" of relation "mytable" does not exist
+select has_column_privilege('mytable','........pg.dropped.2........','select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
+select has_column_privilege('mytable',2::int2,'select');
+ has_column_privilege 
+----------------------
+ t
+(1 row)
+
+revoke select on table mytable from regress_priv_user3;
+select has_column_privilege('mytable',2::int2,'select');
+ has_column_privilege 
+----------------------
+ 
+(1 row)
+
 -- Grant options
 SET SESSION AUTHORIZATION regress_priv_user1;
 CREATE TABLE atest4 (a int);
diff --git a/src/test/regress/sql/privileges.sql b/src/test/regress/sql/privileges.sql
index f7f3bbbeeb6..0c0bba6cf7f 100644
--- a/src/test/regress/sql/privileges.sql
+++ b/src/test/regress/sql/privileges.sql
@@ -715,6 +715,23 @@ from (select oid from pg_class where relname = 'atest1') as t1;
 select has_table_privilege(t1.oid,'trigger')
 from (select oid from pg_class where relname = 'atest1') as t1;
 
+-- has_column_privilege function
+
+-- bad-input checks (as non-super-user)
+select has_column_privilege('pg_authid',NULL,'select');
+select has_column_privilege('pg_authid','nosuchcol','select');
+select has_column_privilege(9999,'nosuchcol','select');
+select has_column_privilege(9999,99::int2,'select');
+select has_column_privilege('pg_authid',99::int2,'select');
+select has_column_privilege(9999,99::int2,'select');
+
+create temp table mytable(f1 int, f2 int, f3 int);
+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');
+revoke select on table mytable from regress_priv_user3;
+select has_column_privilege('mytable',2::int2,'select');
 
 -- Grant options