Re: BUG #19382: Server crash at __nss_database_lookup

Hi All,

I am working on a patch for this.
>

I built a patch on 17.6 postgres version.

The overall issue is:
When ALTER TYPE modifies column types, the type cache updates its
tupDesc_identifier.
However, existing ExpandedRecordHeader instances still reference the old
tupdesc.
When the record is returned and flattened, the output functions expect data
to match the new type definition but receive data in the old format,
causing type confusion (e.g., interpreting an integer as a text pointer).
This was causing a segfault and crashing the server.

In my solution (attached patch), I added convert_record_for_altered_type()
function which detects type changes by comparing er_tupdesc_id against the
current tupDesc_identifier.
When a mismatch is found, it tries to convert each field value to match the
new type definition, if this fails we error out.
convert_record_for_altered_type() function is called in exec_stmt_return()
and exec_stmt_return_next() before returning records.

I tested my patch and see the below output
postgres=# DROP FUNCTION IF EXISTS bar();
DROP FUNCTION
postgres=# DROP TYPE IF EXISTS foo CASCADE;
DROP TYPE
postgres=# DROP FUNCTION IF EXISTS bar1();
DROP FUNCTION
postgres=# DROP TYPE IF EXISTS foo1 CASCADE;
DROP TYPE
postgres=# CREATE TYPE foo AS (a INT, b INT);
CREATE TYPE
postgres=# CREATE FUNCTION bar() RETURNS RECORD AS $$
postgres$# DECLARE
postgres$# r foo := ROW(123, power(2, 30));
postgres$# BEGIN
postgres$# ALTER TYPE foo ALTER ATTRIBUTE b TYPE TEXT;
postgres$# RETURN r;
postgres$# END;
postgres$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
postgres=#
postgres=# SELECT bar();
bar
------------------
(123,1073741824)
(1 row)

postgres=# CREATE TYPE foo1 AS (a INT, b INT);
CREATE TYPE
postgres=#
postgres=# CREATE FUNCTION bar1(OUT r1 foo1) AS $$
postgres$# BEGIN
postgres$# r1 := ROW(1, 2);
postgres$# ALTER TYPE foo1 ALTER ATTRIBUTE b TYPE TEXT;
postgres$# RETURN;
postgres$# END;
postgres$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
postgres=#
postgres=# SELECT bar1();
bar1
-------
(1,2)
(1 row)

postgres=# CREATE TYPE foo2 AS (a INT, b TEXT);
CREATE TYPE
postgres=# CREATE FUNCTION bar2() RETURNS foo2 AS $$
postgres$# DECLARE
postgres$# r foo2 := ROW(1, 'hello');
postgres$# BEGIN
postgres$# ALTER TYPE foo2 ALTER ATTRIBUTE b TYPE INT; -- TEXT → INT
postgres$# RETURN r; -- Should get clean error (not crash)
postgres$# END;
postgres$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
postgres=#
postgres=# SELECT bar2();
ERROR: invalid input syntax for type integer: "hello"
CONTEXT: PL/pgSQL function bar2() line 6 at RETURN
postgres=#