AVRO-4298: [php] Bound allocation when decoding length-prefixed values and collections

lang/php/lib/Datum/AvroIOBinaryDecoder.php

@@ -38,6 +38,14 @@
  */
 class AvroIOBinaryDecoder
 {
+    /**
+     * Reads with a declared length above this many bytes are validated against
+     * the number of bytes actually remaining before allocating, to guard
+     * against an out-of-memory attack from a malicious or truncated input.
+     * Smaller reads skip the check to avoid per-value overhead.
+     */
+    private const MAX_UNCHECKED_READ = 1048576; // 1 MiB
+
     /**
      * @param AvroIO $io object from which to read.
      */
@@ -65,9 +73,39 @@ public function readBoolean(): bool
      */
     public function read(int $len): string
     {
+        if ($len < 0) {
+            // AvroStringIO::read() accepts a negative length and moves the
+            // pointer backwards; reject it before delegating.
+            throw new AvroException("Cannot read a negative number of bytes: {$len}");
+        }
+        if ($len > self::MAX_UNCHECKED_READ) {
+            $remaining = $this->bytesRemaining();
+            if ($len > $remaining) {
+                throw new AvroException("Cannot read {$len} bytes, only {$remaining} remaining.");
+            }
+        }
+
         return $this->io->read($len);
     }
 
+    /**
+     * Number of bytes still available to read, determined by seeking to the end
+     * and restoring the position (which both the string and file IO
+     * implementations support). Used to reject a declared length or collection
+     * block count that exceeds the data actually available before allocating.
+     */
+    public function bytesRemaining(): int
+    {
+        $current = $this->io->tell();
+        $this->io->seek(0, AvroIO::SEEK_END);
+        $end = $this->io->tell();
+        $this->io->seek($current, AvroIO::SEEK_SET);
+
+        // Clamp to 0: AvroStringIO::seek() allows seeking past EOF, which would
+        // otherwise yield a confusing negative "remaining" count.
+        return max(0, $end - $current);
+    }
+
     public function readInt(): int
     {
         return (int) $this->readLong();
@@ -235,28 +273,39 @@ public function skipRecord(AvroRecordSchema $writersSchema, AvroIOBinaryDecoder
 
     public function skipArray(AvroArraySchema $writersSchema, AvroIOBinaryDecoder $decoder): void
     {
+        $minBytes = AvroIODatumReader::collectionElementMinBytes($writersSchema->items());
+        $skipped = 0;
         $blockCount = $decoder->readLong();
         while (0 !== $blockCount) {
             if ($blockCount < 0) {
                 $decoder->skip($this->readLong());
-            }
-            for ($i = 0; $i < $blockCount; $i++) {
-                AvroIODatumReader::skipData($writersSchema->items(), $decoder);
+            } else {
+                AvroIODatumReader::checkSkipCollectionCount($skipped, $blockCount, $minBytes);
+                $skipped += $blockCount;
+                for ($i = 0; $i < $blockCount; $i++) {
+                    AvroIODatumReader::skipData($writersSchema->items(), $decoder);
+                }
             }
             $blockCount = $decoder->readLong();
         }
     }
 
     public function skipMap(AvroMapSchema $writersSchema, AvroIOBinaryDecoder $decoder): void
     {
+        // Map entries always carry a >= 1 byte key, so the minimum is positive.
+        $minBytes = 1 + AvroIODatumReader::collectionElementMinBytes($writersSchema->values());
+        $skipped = 0;
         $blockCount = $decoder->readLong();
         while (0 !== $blockCount) {
             if ($blockCount < 0) {
                 $decoder->skip($this->readLong());
-            }
-            for ($i = 0; $i < $blockCount; $i++) {
-                $decoder->skipString();
-                AvroIODatumReader::skipData($writersSchema->values(), $decoder);
+            } else {
+                AvroIODatumReader::checkSkipCollectionCount($skipped, $blockCount, $minBytes);
+                $skipped += $blockCount;
+                for ($i = 0; $i < $blockCount; $i++) {
+                    $decoder->skipString();
+                    AvroIODatumReader::skipData($writersSchema->values(), $decoder);
+                }
             }
             $blockCount = $decoder->readLong();
         }

lang/php/lib/Datum/AvroIOCollectionSizeException.php

@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * 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.
+ */
+
+declare(strict_types=1);
+
+namespace Apache\Avro\Datum;
+
+use Apache\Avro\AvroException;
+
+/**
+ * Raised when an array or map declares more items than the configured maximum.
+ *
+ * The block count of an array or map is read from the (potentially untrusted or
+ * truncated) input and drives allocation of the resulting collection. This
+ * exception guards against unbounded memory allocation from a very large or
+ * malformed block count.
+ */
+class AvroIOCollectionSizeException extends AvroException
+{
+    public function __construct(int $maxItems)
+    {
+        parent::__construct(
+            sprintf('Cannot read collections larger than %d items.', $maxItems)
+        );
+    }
+}

lang/php/lib/Datum/AvroIODatumReader.php

@@ -43,6 +43,29 @@
  */
 class AvroIODatumReader
 {
+    /**
+     * Name of the environment variable overriding the maximum number of
+     * zero-byte-encoded collection elements (e.g. an array of nulls) to
+     * allocate from a single decode.
+     */
+    public const MAX_COLLECTION_ITEMS_ENV = 'AVRO_MAX_COLLECTION_ITEMS';
+
+    /**
+     * Default maximum number of zero-byte-encoded collection elements to
+     * allocate. Such elements consume no input, so the bytes-remaining check
+     * cannot bound their count; without a cap a tiny payload can declare a huge
+     * block count and exhaust memory. Overridable with the
+     * {@see self::MAX_COLLECTION_ITEMS_ENV} environment variable.
+     */
+    public const DEFAULT_MAX_COLLECTION_ITEMS = 10000000;
+
+    /**
+     * Structural cap on the number of elements in any array or map (an overflow
+     * / defense-in-depth guard), matching the historical Integer.MAX_VALUE - 8
+     * limit. Non-zero-byte elements are also bounded by the bytes remaining.
+     */
+    public const DEFAULT_MAX_COLLECTION_STRUCTURAL = 2147483639;
+
     public function __construct(
         private ?AvroSchema $writersSchema = null,
         private ?AvroSchema $readersSchema = null
@@ -284,12 +307,14 @@ public function readArray(
         AvroIOBinaryDecoder $decoder
     ): array {
         $items = [];
+        $minBytes = self::minBytesPerElement($writersSchema->items());
         $blockCount = $decoder->readLong();
-        while (0 !== $blockCount) {
+        while (0 != $blockCount) {
             if ($blockCount < 0) {
                 $blockCount = -$blockCount;
                 $decoder->readLong(); // Read (and ignore) block size
             }
+            self::ensureCollectionAvailable($decoder, count($items), $blockCount, $minBytes);
             for ($i = 0; $i < $blockCount; $i++) {
                 $items[] = $this->readData(
                     $writersSchema->items(),
@@ -312,6 +337,7 @@ public function readMap(
         AvroIOBinaryDecoder $decoder
     ): array {
         $items = [];
+        $minBytes = 1 + self::minBytesPerElement($writersSchema->values());
         $pair_count = $decoder->readLong();
         while (0 != $pair_count) {
             if ($pair_count < 0) {
@@ -320,6 +346,8 @@ public function readMap(
                 $decoder->readLong();
             }
 
+            // Map keys are strings (>= 1 byte length prefix) plus the value.
+            self::ensureCollectionAvailable($decoder, count($items), $pair_count, $minBytes);
             for ($i = 0; $i < $pair_count; $i++) {
                 $key = $decoder->readString();
                 $items[$key] = $this->readData(
@@ -530,6 +558,34 @@ public function readDefaultValue(AvroSchema $fieldSchema, mixed $defaultValue):
         }
     }
 
+    /**
+     * Minimum on-wire size of a collection element schema. Exposed for the skip
+     * path, which lives in the decoder.
+     */
+    public static function collectionElementMinBytes(AvroSchema $schema): int
+    {
+        return self::minBytesPerElement($schema);
+    }
+
+    /**
+     * Bounds the cumulative number of elements skipped in an array or map, so a
+     * huge block of zero-byte elements cannot loop unboundedly (a CPU
+     * exhaustion) even though skipping allocates nothing.
+     *
+     * @throws AvroIOCollectionSizeException if the limit is exceeded
+     */
+    public static function checkSkipCollectionCount(int $existing, int $count, int $minBytes): void
+    {
+        if ($count <= 0) {
+            return;
+        }
+        [$zeroByteLimit, $structuralLimit] = self::collectionLimits();
+        $limit = $minBytes > 0 ? $structuralLimit : $zeroByteLimit;
+        if ($count > $limit || $existing > $limit - $count) {
+            throw new AvroIOCollectionSizeException($limit);
+        }
+    }
+
     private function readDecimal(string $bytes, int $scale): string
     {
         $mostSignificantBit = ord($bytes[0]) & 0x80;
@@ -538,4 +594,118 @@ private function readDecimal(string $bytes, int $scale): string
 
         return (string) ($scale > 0 ? ($int / (10 ** $scale)) : $int);
     }
+
+    /**
+     * Minimum number of bytes a single value of the given schema can occupy on
+     * the wire. Used to reject an array/map block count that could not be backed
+     * by the bytes remaining. It returns 0 for any schema that can encode to
+     * zero bytes: the null primitive, but also a record with no fields or whose
+     * fields all encode to zero bytes. A zero return disables the collection
+     * check for that element type (so, e.g., an array of nulls is not falsely
+     * rejected). Types that cannot be resolved cheaply default to 1.
+     *
+     * @param array<int, bool> $visited
+     */
+    private static function minBytesPerElement(mixed $schema, array $visited = []): int
+    {
+        $type = $schema instanceof AvroSchema ? $schema->type() : $schema;
+        // Named/complex field types may nest a schema object; unwrap one level.
+        if ($type instanceof AvroSchema) {
+            return self::minBytesPerElement($type, $visited);
+        }
+        if (!is_string($type)) {
+            return 1;
+        }
+        switch ($type) {
+            case AvroSchema::NULL_TYPE:
+                return 0;
+            case AvroSchema::FLOAT_TYPE:
+                return 4;
+            case AvroSchema::DOUBLE_TYPE:
+                return 8;
+            case AvroSchema::FIXED_SCHEMA:
+                return $schema instanceof AvroFixedSchema ? $schema->size() : 1;
+            case AvroSchema::RECORD_SCHEMA:
+            case AvroSchema::ERROR_SCHEMA:
+                if (!$schema instanceof AvroRecordSchema) {
+                    return 1;
+                }
+                $id = spl_object_id($schema);
+                if (isset($visited[$id])) {
+                    return 1; // self-referencing schema: safe lower bound of 1 byte
+                }
+                $visited[$id] = true;
+                $total = 0;
+                foreach ($schema->fields() as $field) {
+                    $total += self::minBytesPerElement($field, $visited);
+                }
+
+                return $total;
+            default:
+                // boolean, int, long, bytes, string, enum, union, array, map:
+                // all encode to at least one byte.
+                return 1;
+        }
+    }
+
+    /**
+     * Returns the configured collection limits as [zeroByteLimit, structuralLimit].
+     * AVRO_MAX_COLLECTION_ITEMS, when a non-negative integer, caps both.
+     *
+     * @return array{int, int}
+     */
+    private static function collectionLimits(): array
+    {
+        $value = getenv(self::MAX_COLLECTION_ITEMS_ENV);
+        if (false !== $value && '' !== $value && preg_match('/^-?\d+$/', $value)) {
+            $parsed = (int) $value;
+            if ($parsed >= 0) {
+                return [$parsed, $parsed];
+            }
+        }
+
+        return [self::DEFAULT_MAX_COLLECTION_ITEMS, self::DEFAULT_MAX_COLLECTION_STRUCTURAL];
+    }
+
+    /**
+     * Rejects a collection (array or map) block that could not be backed by the
+     * input, before iterating.
+     *
+     * For elements with a positive minimum on-wire size, the declared count is
+     * checked against the bytes remaining and a structural cap. For zero-byte
+     * elements (e.g. an array of nulls), which consume no input and so cannot be
+     * bounded by the bytes remaining, the cumulative count is checked against the
+     * tighter zero-byte limit.
+     *
+     * @throws AvroException                 if the bytes-remaining check fails
+     * @throws AvroIOCollectionSizeException if a size limit is exceeded
+     */
+    private static function ensureCollectionAvailable(
+        AvroIOBinaryDecoder $decoder,
+        int $existing,
+        int $count,
+        int $minBytesPerElement
+    ): void {
+        if ($count <= 0) {
+            return;
+        }
+        [$zeroByteLimit, $structuralLimit] = self::collectionLimits();
+        if ($minBytesPerElement > 0) {
+            $remaining = $decoder->bytesRemaining();
+            if ($count > intdiv($remaining, $minBytesPerElement)) {
+                throw new AvroException(
+                    "Collection claims {$count} elements with at least {$minBytesPerElement} "
+                    ."bytes each, but only {$remaining} bytes are available."
+                );
+            }
+            if ($count > $structuralLimit || $existing > $structuralLimit - $count) {
+                throw new AvroIOCollectionSizeException($structuralLimit);
+            }
+
+            return;
+        }
+        if ($count > $zeroByteLimit || $existing > $zeroByteLimit - $count) {
+            throw new AvroIOCollectionSizeException($zeroByteLimit);
+        }
+    }
 }

lang/php/lib/autoload.php

@@ -33,6 +33,7 @@
 
 include __DIR__.'/Datum/AvroIOBinaryDecoder.php';
 include __DIR__.'/Datum/AvroIOBinaryEncoder.php';
+include __DIR__.'/Datum/AvroIOCollectionSizeException.php';
 include __DIR__.'/Datum/AvroIODatumReader.php';
 include __DIR__.'/Datum/AvroIODatumWriter.php';
 include __DIR__.'/Datum/AvroIOSchemaMatchException.php';