AVRO-4344: [C] Reject out-of-range enum ordinal instead of returning an uninitialized pointer

lang/c/src/schema.c

@@ -538,7 +538,14 @@ const char *avro_schema_enum_get(const avro_schema_t enump,
 		st_data_t data;
 		char *sym;
 	} val;
-	st_lookup(avro_schema_to_enum(enump)->symbols, index, &val.data);
+	/*
+	 * Return NULL for an unknown index rather than an uninitialized
+	 * pointer: st_lookup() leaves val.data untouched when the key is
+	 * not found.
+	 */
+	if (!st_lookup(avro_schema_to_enum(enump)->symbols, index, &val.data)) {
+		return NULL;
+	}
 	return val.sym;
 }
 

lang/c/src/value-read.c

@@ -329,10 +329,23 @@ read_value(avro_reader_t reader, avro_value_t *dest)
 
 		case AVRO_ENUM:
 		{
+			avro_schema_t  schema = avro_value_get_schema(dest);
 			int64_t  val;
 			check_prefix(rval, avro_binary_encoding.
 				     read_long(reader, &val),
 				     "Cannot read enum value: ");
+			/*
+			 * Reject an out-of-range ordinal read from the input
+			 * before it is used to look up a symbol; otherwise the
+			 * lookup fails and an uninitialized pointer would be
+			 * returned to the caller (see avro_schema_enum_get).
+			 */
+			if (val < 0 ||
+			    val >= avro_schema_enum_number_of_symbols(schema)) {
+				avro_set_error("Enum value %ld is out of range",
+					       (long) val);
+				return EINVAL;
+			}
 			return avro_value_set_enum(dest, val);
 		}
 

lang/c/tests/CMakeLists.txt

@@ -88,3 +88,4 @@ add_avro_test_checkmem(test_avro_1691)
 add_avro_test_checkmem(test_avro_1906)
 add_avro_test_checkmem(test_avro_1904)
 add_avro_test_checkmem(test_avro_4246)
+add_avro_test_checkmem(test_avro_4344)

lang/c/tests/test_avro_4344.c

@@ -0,0 +1,95 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied.  See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+/*
+ * AVRO-4344: reading an out-of-range enum ordinal must return an error
+ * rather than continuing with an out-of-range index (which previously led
+ * avro_schema_enum_get() to return an uninitialized pointer).
+ */
+
+#include <avro.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static avro_schema_t
+make_enum_schema(void)
+{
+	/* Two symbols -> valid ordinals are 0 and 1. */
+	avro_schema_t  schema = avro_schema_enum("suit");
+	avro_schema_enum_symbol_append(schema, "SPADES");
+	avro_schema_enum_symbol_append(schema, "HEARTS");
+	return schema;
+}
+
+static int
+read_enum(avro_value_iface_t *iface, const char *buf, size_t len)
+{
+	avro_reader_t  reader = avro_reader_memory(buf, len);
+	avro_value_t   value;
+	int            rval;
+
+	avro_generic_value_new(iface, &value);
+	rval = avro_value_read(reader, &value);
+	avro_value_decref(&value);
+	avro_reader_free(reader);
+	return rval;
+}
+
+int main(void)
+{
+	avro_schema_t       schema = make_enum_schema();
+	avro_value_iface_t *iface = avro_generic_class_from_schema(schema);
+
+	/* A valid ordinal (1, zig-zag 0x02) must read successfully. */
+	{
+		const char  buf[] = { 0x02 };
+		if (read_enum(iface, buf, sizeof(buf)) != 0) {
+			fprintf(stderr, "Valid enum ordinal failed to read: %s\n",
+				avro_strerror());
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	/* An out-of-range positive ordinal (5, zig-zag 0x0A) must error. */
+	{
+		const char  buf[] = { 0x0a };
+		if (read_enum(iface, buf, sizeof(buf)) == 0) {
+			fprintf(stderr, "Out-of-range enum ordinal was accepted\n");
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	/* A negative ordinal (-1, zig-zag 0x01) must error. */
+	{
+		const char  buf[] = { 0x01 };
+		if (read_enum(iface, buf, sizeof(buf)) == 0) {
+			fprintf(stderr, "Negative enum ordinal was accepted\n");
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	/* avro_schema_enum_get() returns NULL (not garbage) for a bad index. */
+	if (avro_schema_enum_get(schema, 99) != NULL) {
+		fprintf(stderr, "avro_schema_enum_get did not return NULL for "
+			"an out-of-range index\n");
+		exit(EXIT_FAILURE);
+	}
+
+	avro_value_iface_decref(iface);
+	avro_schema_decref(schema);
+	exit(EXIT_SUCCESS);
+}