IS JSON/JSON(): Protect against expressions uncoercible to text

transformJsonParseArg() was not careful enough on generation of
transformed expressions when starting from expressions that are not
coercible to text but are in the string type category: it failed to
verify that coerce_to_target_type() succeeds, and returned a NULL
pointer.  This leads to a later NULL dereference and crash at executor
time.

This escaped noticed because it cannot happen for built-in types, all of
which have casts to text.  Only user-created types are potentially
problematic.

Fix by raising an error when a cast to text doesn't exist.

This mistake came in with commit 6ee30209a6f1.

Author: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Reported-by: Chi Zhang <798604270@qq.com>
Reviewed-by: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Backpatch-through: 16
Discussion: https://postgr.es/m/19491-7aafc221ec63f288@postgresql.org

diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index e2d9e9be41a65f79d7da662b234b3f873e2e290d..bc48966c5d1e141fbb6a0b5326feefc639711815 100644 (file)
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -988,6 +988,8 @@ makeJsonIsPredicate(Node *expr, JsonFormat *format, JsonValueType item_type,
 {
        JsonIsPredicate *n = makeNode(JsonIsPredicate);
 
+       Assert(expr != NULL);
+
        n->expr = expr;
        n->format = format;
        n->item_type = item_type;

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index b6d30ddc29823ce25d60616ef0a2a3e638abab5a..a00b46a25ca00f5bd4b5ea64f4817522b7365553 100644 (file)
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -4088,10 +4088,20 @@ transformJsonParseArg(ParseState *pstate, Node *jsexpr, JsonFormat *format,
 
                if (*exprtype == UNKNOWNOID || typcategory == TYPCATEGORY_STRING)
                {
+                       int                     location = exprLocation(expr);
+
                        expr = coerce_to_target_type(pstate, (Node *) expr, *exprtype,
                                                                                 TEXTOID, -1,
                                                                                 COERCION_IMPLICIT,
                                                                                 COERCE_IMPLICIT_CAST, -1);
+                       if (expr == NULL)
+                               ereport(ERROR,
+                                               errcode(ERRCODE_CANNOT_COERCE),
+                                               errmsg("cannot cast type %s to %s",
+                                                          format_type_be(*exprtype),
+                                                          format_type_be(TEXTOID)),
+                                               parser_errposition(pstate, location));
+
                        *exprtype = TEXTOID;
                }
 

diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index 625acf3019a3818f5966d6486f9703ec3fa1d19d..6b0d881550839951025776974a0d1c50a7bfbe0e 100644 (file)
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -1148,6 +1148,44 @@ SELECT NULL::bytea IS JSON;
 
 SELECT NULL::int IS JSON;
 ERROR:  cannot use type integer in IS JSON predicate
+-- A user-defined string-category type with no implicit cast to text must
+-- produce a clean error rather than crash for IS JSON / JSON() input
+-- (per bug #19491).
+CREATE FUNCTION sqljson_mystr_in(cstring) RETURNS sqljson_mystr
+       AS 'textin' LANGUAGE internal IMMUTABLE STRICT;
+NOTICE:  type "sqljson_mystr" is not yet defined
+DETAIL:  Creating a shell type definition.
+CREATE FUNCTION sqljson_mystr_out(sqljson_mystr) RETURNS cstring
+       AS 'textout' LANGUAGE internal IMMUTABLE STRICT;
+NOTICE:  argument type sqljson_mystr is only a shell
+LINE 1: CREATE FUNCTION sqljson_mystr_out(sqljson_mystr) RETURNS cst...
+                                          ^
+CREATE TYPE sqljson_mystr (
+       INPUT = sqljson_mystr_in,
+       OUTPUT = sqljson_mystr_out,
+       LIKE = text,
+       CATEGORY = 'S'
+);
+SELECT '{"a":1}'::sqljson_mystr IS JSON;                -- error
+ERROR:  cannot cast type sqljson_mystr to text
+LINE 1: SELECT '{"a":1}'::sqljson_mystr IS JSON;
+               ^
+SELECT JSON('{"a":1}'::sqljson_mystr WITH UNIQUE KEYS); -- error
+ERROR:  cannot cast type sqljson_mystr to text
+LINE 1: SELECT JSON('{"a":1}'::sqljson_mystr WITH UNIQUE KEYS);
+                    ^
+-- An implicit cast to text lets the same query work normally.
+CREATE CAST (sqljson_mystr AS text) WITHOUT FUNCTION AS IMPLICIT;
+SELECT '{"a":1}'::sqljson_mystr IS JSON;
+ ?column? 
+----------
+ t
+(1 row)
+
+\set VERBOSITY terse
+DROP TYPE sqljson_mystr CASCADE;
+NOTICE:  drop cascades to 3 other objects
+\set VERBOSITY default
 SELECT '' IS JSON;
  ?column? 
 ----------

diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index 343d344d2707f40bbb4f9acd17b0ec5e0772b545..0b77deb3b24b77b53faff38f1a4a6c7aeb294874 100644 (file)
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -395,6 +395,28 @@ SELECT NULL::text IS JSON;
 SELECT NULL::bytea IS JSON;
 SELECT NULL::int IS JSON;
 
+-- A user-defined string-category type with no implicit cast to text must
+-- produce a clean error rather than crash for IS JSON / JSON() input
+-- (per bug #19491).
+CREATE FUNCTION sqljson_mystr_in(cstring) RETURNS sqljson_mystr
+       AS 'textin' LANGUAGE internal IMMUTABLE STRICT;
+CREATE FUNCTION sqljson_mystr_out(sqljson_mystr) RETURNS cstring
+       AS 'textout' LANGUAGE internal IMMUTABLE STRICT;
+CREATE TYPE sqljson_mystr (
+       INPUT = sqljson_mystr_in,
+       OUTPUT = sqljson_mystr_out,
+       LIKE = text,
+       CATEGORY = 'S'
+);
+SELECT '{"a":1}'::sqljson_mystr IS JSON;                -- error
+SELECT JSON('{"a":1}'::sqljson_mystr WITH UNIQUE KEYS); -- error
+-- An implicit cast to text lets the same query work normally.
+CREATE CAST (sqljson_mystr AS text) WITHOUT FUNCTION AS IMPLICIT;
+SELECT '{"a":1}'::sqljson_mystr IS JSON;
+\set VERBOSITY terse
+DROP TYPE sqljson_mystr CASCADE;
+\set VERBOSITY default
+
 SELECT '' IS JSON;
 
 SELECT bytea '\x00' IS JSON;