Tighten array dimensionality checks in Perl -> SQL array conversion.

plperl_array_to_datum() wasn't sufficiently careful about checking
that nested lists represent a rectangular array structure; it would
accept inputs such as "[1, []]".  This is a bit related to the
PL/Python bug fixed in commit 81eaaf65e, but it doesn't seem to
provide any direct route to a memory stomp.  Instead the likely
failure mode is for makeMdArrayResult to be passed fewer Datums than
the claimed array dimensionality requires, possibly leading to a wild
pointer dereference and SIGSEGV.

Per report from Alexander Lakhin.  It's been broken for a long
time, so back-patch to all supported branches.

Discussion: https://postgr.es/m/5ebae5e4-d401-fadf-8585-ac3eaf53219c@gmail.com

src/pl/plperl/expected/plperl_array.out

@@ -215,6 +215,49 @@ select plperl_arrays_inout_l('{{1}, {2}, {3}}');
  {{1},{2},{3}}
 (1 row)
 
+-- check output of multi-dimensional arrays
+CREATE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [['a'], ['b'], ['c']];
+$$ LANGUAGE plperl;
+select plperl_md_array_out();
+ plperl_md_array_out 
+---------------------
+ {{a},{b},{c}}
+(1 row)
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[], []];
+$$ LANGUAGE plperl;
+select plperl_md_array_out();
+ plperl_md_array_out 
+---------------------
+ {}
+(1 row)
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[], [1]];
+$$ LANGUAGE plperl;
+select plperl_md_array_out();  -- fail
+ERROR:  multidimensional arrays must have array expressions with matching dimensions
+CONTEXT:  PL/Perl function "plperl_md_array_out"
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[], 1];
+$$ LANGUAGE plperl;
+select plperl_md_array_out();  -- fail
+ERROR:  multidimensional arrays must have array expressions with matching dimensions
+CONTEXT:  PL/Perl function "plperl_md_array_out"
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [1, []];
+$$ LANGUAGE plperl;
+select plperl_md_array_out();  -- fail
+ERROR:  multidimensional arrays must have array expressions with matching dimensions
+CONTEXT:  PL/Perl function "plperl_md_array_out"
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[1], [[]]];
+$$ LANGUAGE plperl;
+select plperl_md_array_out();  -- fail
+ERROR:  multidimensional arrays must have array expressions with matching dimensions
+CONTEXT:  PL/Perl function "plperl_md_array_out"
 -- make sure setof works
 create or replace function perl_setof_array(integer[]) returns setof integer[] language plperl as $$
 	my $arr = shift;

src/pl/plperl/plperl.c

@@ -275,9 +275,9 @@ static Datum plperl_sv_to_datum(SV *sv, Oid typid, int32 typmod,
 								bool *isnull);
 static void _sv_to_datum_finfo(Oid typid, FmgrInfo *finfo, Oid *typioparam);
 static Datum plperl_array_to_datum(SV *src, Oid typid, int32 typmod);
-static void array_to_datum_internal(AV *av, ArrayBuildState *astate,
+static void array_to_datum_internal(AV *av, ArrayBuildState **astatep,
 									int *ndims, int *dims, int cur_depth,
-									Oid arraytypid, Oid elemtypid, int32 typmod,
+									Oid elemtypid, int32 typmod,
 									FmgrInfo *finfo, Oid typioparam);
 static Datum plperl_hash_to_datum(SV *src, TupleDesc td);
 
@@ -1163,11 +1163,16 @@ get_perl_array_ref(SV *sv)
 
 /*
  * helper function for plperl_array_to_datum, recurses for multi-D arrays
+ *
+ * The ArrayBuildState is created only when we first find a scalar element;
+ * if we didn't do it like that, we'd need some other convention for knowing
+ * whether we'd already found any scalars (and thus the number of dimensions
+ * is frozen).
  */
 static void
-array_to_datum_internal(AV *av, ArrayBuildState *astate,
+array_to_datum_internal(AV *av, ArrayBuildState **astatep,
 						int *ndims, int *dims, int cur_depth,
-						Oid arraytypid, Oid elemtypid, int32 typmod,
+						Oid elemtypid, int32 typmod,
 						FmgrInfo *finfo, Oid typioparam)
 {
 	dTHX;
@@ -1187,28 +1192,34 @@ array_to_datum_internal(AV *av, ArrayBuildState *astate,
 		{
 			AV		   *nav = (AV *) SvRV(sav);
 
-			/* dimensionality checks */
-			if (cur_depth + 1 > MAXDIM)
-				ereport(ERROR,
-						(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-						 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
-								cur_depth + 1, MAXDIM)));
-
 			/* set size when at first element in this level, else compare */
 			if (i == 0 && *ndims == cur_depth)
 			{
+				/* array after some scalars at same level? */
+				if (*astatep != NULL)
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
+							 errmsg("multidimensional arrays must have array expressions with matching dimensions")));
+				/* too many dimensions? */
+				if (cur_depth + 1 > MAXDIM)
+					ereport(ERROR,
+							(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+							 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
+									cur_depth + 1, MAXDIM)));
+				/* OK, add a dimension */
 				dims[*ndims] = av_len(nav) + 1;
 				(*ndims)++;
 			}
-			else if (av_len(nav) + 1 != dims[cur_depth])
+			else if (cur_depth >= *ndims ||
+					 av_len(nav) + 1 != dims[cur_depth])
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
 						 errmsg("multidimensional arrays must have array expressions with matching dimensions")));
 
 			/* recurse to fetch elements of this sub-array */
-			array_to_datum_internal(nav, astate,
+			array_to_datum_internal(nav, astatep,
 									ndims, dims, cur_depth + 1,
-									arraytypid, elemtypid, typmod,
+									elemtypid, typmod,
 									finfo, typioparam);
 		}
 		else
@@ -1230,7 +1241,13 @@ array_to_datum_internal(AV *av, ArrayBuildState *astate,
 									 typioparam,
 									 &isnull);
 
-			(void) accumArrayResult(astate, dat, isnull,
+			/* Create ArrayBuildState if we didn't already */
+			if (*astatep == NULL)
+				*astatep = initArrayResult(elemtypid,
+										   CurrentMemoryContext, true);
+
+			/* ... and save the element value in it */
+			(void) accumArrayResult(*astatep, dat, isnull,
 									elemtypid, CurrentMemoryContext);
 		}
 	}
@@ -1243,7 +1260,8 @@ static Datum
 plperl_array_to_datum(SV *src, Oid typid, int32 typmod)
 {
 	dTHX;
-	ArrayBuildState *astate;
+	AV		   *nav = (AV *) SvRV(src);
+	ArrayBuildState *astate = NULL;
 	Oid			elemtypid;
 	FmgrInfo	finfo;
 	Oid			typioparam;
@@ -1259,21 +1277,19 @@ plperl_array_to_datum(SV *src, Oid typid, int32 typmod)
 				 errmsg("cannot convert Perl array to non-array type %s",
 						format_type_be(typid))));
 
-	astate = initArrayResult(elemtypid, CurrentMemoryContext, true);
-
 	_sv_to_datum_finfo(elemtypid, &finfo, &typioparam);
 
 	memset(dims, 0, sizeof(dims));
-	dims[0] = av_len((AV *) SvRV(src)) + 1;
+	dims[0] = av_len(nav) + 1;
 
-	array_to_datum_internal((AV *) SvRV(src), astate,
+	array_to_datum_internal(nav, &astate,
 							&ndims, dims, 1,
-							typid, elemtypid, typmod,
+							elemtypid, typmod,
 							&finfo, typioparam);
 
 	/* ensure we get zero-D array for no inputs, as per PG convention */
-	if (dims[0] <= 0)
+	if (astate == NULL)
-		ndims = 0;
+		return PointerGetDatum(construct_empty_array(elemtypid));
 
 	for (i = 0; i < ndims; i++)
 		lbs[i] = 1;

src/pl/plperl/sql/plperl_array.sql

@@ -159,6 +159,43 @@ $$ LANGUAGE plperl;
 
 select plperl_arrays_inout_l('{{1}, {2}, {3}}');
 
+-- check output of multi-dimensional arrays
+CREATE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [['a'], ['b'], ['c']];
+$$ LANGUAGE plperl;
+
+select plperl_md_array_out();
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[], []];
+$$ LANGUAGE plperl;
+
+select plperl_md_array_out();
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[], [1]];
+$$ LANGUAGE plperl;
+
+select plperl_md_array_out();  -- fail
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[], 1];
+$$ LANGUAGE plperl;
+
+select plperl_md_array_out();  -- fail
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [1, []];
+$$ LANGUAGE plperl;
+
+select plperl_md_array_out();  -- fail
+
+CREATE OR REPLACE FUNCTION plperl_md_array_out() RETURNS text[] AS $$
+	return [[1], [[]]];
+$$ LANGUAGE plperl;
+
+select plperl_md_array_out();  -- fail
+
 -- make sure setof works
 create or replace function perl_setof_array(integer[]) returns setof integer[] language plperl as $$
 	my $arr = shift;