Fix Assert failure in XMLTABLE parser

In an XMLTABLE expression, columns can be marked NOT NULL, and the
parser internally fabricates an option named "is_not_null" to
represent this.  However, the parser also allows users to specify
arbitrary option names.  This creates a conflict: a user can
explicitly use "is_not_null" as an option name and assign it a
non-Boolean value, which violates internal assumptions and triggers an
assertion failure.

To fix, this patch checks whether a user-supplied name collides with
the internally reserved option name and raises an error if so.
Additionally, the internal name is renamed to "__pg__is_not_null" to
further reduce the risk of collision with user-defined names.

Reported-by: Евгений Горбанев <gorbanyoves@basealt.ru>
Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@kurilemu.de>
Discussion: https://postgr.es/m/6bac9886-65bf-4cec-96bd-e304159f28db@basealt.ru
Backpatch-through: 15

5 files changed, 25 insertions, 4 deletions

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 8379e48c97b..c77060c2cea 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -13820,7 +13820,7 @@ xmltable_column_el:
 										 parser_errposition(defel->location)));
 							fc->colexpr = defel->arg;
 						}
-						else if (strcmp(defel->defname, "is_not_null") == 0)
+						else if (strcmp(defel->defname, "__pg__is_not_null") == 0)
 						{
 							if (nullability_seen)
 								ereport(ERROR,
@@ -13863,13 +13863,20 @@ xmltable_column_option_list:
 
 xmltable_column_option_el:
 			IDENT b_expr
-				{ $$ = makeDefElem($1, $2, @1); }
+				{
+					if (strcmp($1, "__pg__is_not_null") == 0)
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("option name \"%s\" cannot be used in XMLTABLE", $1),
+								 parser_errposition(@1)));
+					$$ = makeDefElem($1, $2, @1);
+				}
 			| DEFAULT b_expr
 				{ $$ = makeDefElem("default", $2, @1); }
 			| NOT NULL_P
-				{ $$ = makeDefElem("is_not_null", (Node *) makeBoolean(true), @1); }
+				{ $$ = makeDefElem("__pg__is_not_null", (Node *) makeBoolean(true), @1); }
 			| NULL_P
-				{ $$ = makeDefElem("is_not_null", (Node *) makeBoolean(false), @1); }
+				{ $$ = makeDefElem("__pg__is_not_null", (Node *) makeBoolean(false), @1); }
 		;
 
 xml_namespace_list:
diff --git a/src/test/regress/expected/xml.out b/src/test/regress/expected/xml.out
index f9b7ec0bab8..79054b75311 100644
--- a/src/test/regress/expected/xml.out
+++ b/src/test/regress/expected/xml.out
@@ -1139,6 +1139,10 @@ EXPLAIN (COSTS OFF, VERBOSE) SELECT * FROM xmltableview1;
 -- errors
 SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp) AS f (v1, v2);
 ERROR:  XMLTABLE function has 1 columns available but 2 columns specified
+SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_not_null 1) AS f (v1);
+ERROR:  option name "__pg__is_not_null" cannot be used in XMLTABLE
+LINE 1: ...MLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_n...
+                                                             ^
 -- XMLNAMESPACES tests
 SELECT * FROM XMLTABLE(XMLNAMESPACES('http://x.y' AS zz),
                       '/zz:rows/zz:row'
diff --git a/src/test/regress/expected/xml_1.out b/src/test/regress/expected/xml_1.out
index 5b28ea01eea..abf27626a21 100644
--- a/src/test/regress/expected/xml_1.out
+++ b/src/test/regress/expected/xml_1.out
@@ -876,6 +876,10 @@ EXPLAIN (COSTS OFF, VERBOSE) SELECT * FROM xmltableview1;
 -- errors
 SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp) AS f (v1, v2);
 ERROR:  XMLTABLE function has 1 columns available but 2 columns specified
+SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_not_null 1) AS f (v1);
+ERROR:  option name "__pg__is_not_null" cannot be used in XMLTABLE
+LINE 1: ...MLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_n...
+                                                             ^
 -- XMLNAMESPACES tests
 SELECT * FROM XMLTABLE(XMLNAMESPACES('http://x.y' AS zz),
                       '/zz:rows/zz:row'
diff --git a/src/test/regress/expected/xml_2.out b/src/test/regress/expected/xml_2.out
index 044a4917d86..23e0c14a2d2 100644
--- a/src/test/regress/expected/xml_2.out
+++ b/src/test/regress/expected/xml_2.out
@@ -1125,6 +1125,10 @@ EXPLAIN (COSTS OFF, VERBOSE) SELECT * FROM xmltableview1;
 -- errors
 SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp) AS f (v1, v2);
 ERROR:  XMLTABLE function has 1 columns available but 2 columns specified
+SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_not_null 1) AS f (v1);
+ERROR:  option name "__pg__is_not_null" cannot be used in XMLTABLE
+LINE 1: ...MLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_n...
+                                                             ^
 -- XMLNAMESPACES tests
 SELECT * FROM XMLTABLE(XMLNAMESPACES('http://x.y' AS zz),
                       '/zz:rows/zz:row'
diff --git a/src/test/regress/sql/xml.sql b/src/test/regress/sql/xml.sql
index e908b6c3957..83c5b73d8d3 100644
--- a/src/test/regress/sql/xml.sql
+++ b/src/test/regress/sql/xml.sql
@@ -387,6 +387,8 @@ EXPLAIN (COSTS OFF, VERBOSE) SELECT * FROM xmltableview1;
 -- errors
 SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp) AS f (v1, v2);
 
+SELECT * FROM XMLTABLE (ROW () PASSING null COLUMNS v1 timestamp __pg__is_not_null 1) AS f (v1);
+
 -- XMLNAMESPACES tests
 SELECT * FROM XMLTABLE(XMLNAMESPACES('http://x.y' AS zz),
                       '/zz:rows/zz:row'