ext/standard: limit maximum number of filter chains

NEWS

@@ -21,6 +21,9 @@ PHP                                                                        NEWS
     ReflectionAttribute::getShortName(). (Girgias)
 
 - Standard:
+  . Added the "filter.max_filter_count" stream context option for php://filter
+    URLs. Using more than 16 filters without configuring this option is now
+    deprecated. (Sjoerd Langkemper)
   . The following functions now raise a ValueError when the $filename argument
     contains NUL bytes: fileperms(), fileinode(), filesize(), fileowner(),
     filegroup(), fileatime(), filemtime(), filectime(), filetype(),

UPGRADING

@@ -363,6 +363,11 @@ PHP 8.6 UPGRADE NOTES
     internal API. It is controlled using error_mode, error_store and
     error_handler stream context options.
     RFC: https://wiki.php.net/rfc/stream_errors
+  . Added the "filter.max_filter_count" stream context option for php://filter
+    URLs. When set, opening the stream fails with a warning if the URL would
+    add more filters than the configured value. Negative values disable the
+    check.
+    RFC: https://wiki.php.net/rfc/limit-maximum-number-of-filter-chains
   . Added stream socket context option so_reuseaddr that allows disabling
     address reuse (SO_REUSEADDR) and explicitly uses SO_EXCLUSIVEADDRUSE on
     Windows.
@@ -413,6 +418,12 @@ PHP 8.6 UPGRADE NOTES
     is no longer maintained.
     RFC: https://wiki.php.net/rfc/eol-oniguruma
 
+- Standard:
+  . Using more than 16 filters in a php://filter URL without configuring the
+    "filter.max_filter_count" stream context option now emits an E_DEPRECATED
+    warning. Use stream_filter_append() or configure this option explicitly.
+    RFC: https://wiki.php.net/rfc/limit-maximum-number-of-filter-chains
+
 ========================================
 5. Changed Functions
 ========================================

ext/standard/php_fopen_wrapper.c

@@ -144,13 +144,38 @@ static const php_stream_ops php_stream_input_ops = {
 	NULL  /* set_option */
 };
 
-static void php_stream_apply_filter_list(php_stream *stream, char *filterlist, int read_chain, int write_chain) /* {{{ */
+static const zend_long max_filter_count_default = 16;
+
+static zend_result php_stream_apply_filter_list(php_stream *stream, char *filterlist, int read_chain, int write_chain, php_stream_context *context) /* {{{ */
 {
 	char *p, *token = NULL;
 	php_stream_filter *temp_filter;
 
+	zend_long max_filter_count = max_filter_count_default;
+	bool max_filter_count_configured = false;
+	if (context != NULL) {
+		zval *option_val = php_stream_context_get_option(context, "filter", "max_filter_count");
+		if (option_val) {
+			max_filter_count = zval_get_long(option_val);
+			max_filter_count_configured = true;
+		}
+	}
+
 	p = php_strtok_r(filterlist, "|", &token);
 	while (p) {
+		zend_long read_count = read_chain ? stream->readfilters.num_filters : 0;
+		zend_long write_count = write_chain ? stream->writefilters.num_filters : 0;
+
+		if (read_count == max_filter_count || write_count == max_filter_count) {
+			if (max_filter_count_configured) {
+				return FAILURE;
+			} else {
+				// No max_filter_count configured; raise deprecation error if over default
+				zend_error(E_DEPRECATED, "Using more than " ZEND_LONG_FMT " filters in a php://filter URL is deprecated, "
+					"set this limit using the stream context option max_filter_count, or use stream_filter_append", max_filter_count_default);
+			}
+		}
+
 		php_url_decode(p, strlen(p));
 		if (read_chain) {
 			if ((temp_filter = php_stream_filter_create(p, NULL, php_stream_is_persistent(stream)))) {
@@ -172,6 +197,7 @@ static void php_stream_apply_filter_list(php_stream *stream, char *filterlist, i
 		}
 		p = php_strtok_r(NULL, "|", &token);
 	}
+	return SUCCESS;
 }
 /* }}} */
 
@@ -362,17 +388,23 @@ static php_stream * php_stream_url_wrap_php(php_stream_wrapper *wrapper, const c
 			return NULL;
 		}
 
+		zend_result safl_result = SUCCESS;
 		*p = '\0';
 
 		p = php_strtok_r(pathdup + 1, "/", &token);
 		while (p) {
 			if (!strncasecmp(p, "read=", 5)) {
-				php_stream_apply_filter_list(stream, p + 5, 1, 0);
+				safl_result = php_stream_apply_filter_list(stream, p + 5, 1, 0, context);
 			} else if (!strncasecmp(p, "write=", 6)) {
-				php_stream_apply_filter_list(stream, p + 6, 0, 1);
+				safl_result = php_stream_apply_filter_list(stream, p + 6, 0, 1, context);
 			} else {
-				php_stream_apply_filter_list(stream, p, mode_rw & PHP_STREAM_FILTER_READ, mode_rw & PHP_STREAM_FILTER_WRITE);
+				safl_result = php_stream_apply_filter_list(stream, p, mode_rw & PHP_STREAM_FILTER_READ, mode_rw & PHP_STREAM_FILTER_WRITE, context);
 			}
+
+			if (safl_result == FAILURE) {
+				break;
+			}
+
 			p = php_strtok_r(NULL, "/", &token);
 		}
 		efree(pathdup);
@@ -382,6 +414,13 @@ static php_stream * php_stream_url_wrap_php(php_stream_wrapper *wrapper, const c
 			return NULL;
 		}
 
+		if (safl_result == FAILURE) {
+			php_stream_wrapper_log_warn(wrapper, context, options,
+				PathTooLong, "too many filters");
+			php_stream_close(stream);
+			return NULL;
+		}
+
 		return stream;
 	} else {
 		/* invalid php://thingy */

ext/standard/tests/filters/max_filter_chain.phpt

@@ -0,0 +1,144 @@
+--TEST--
+At most 16 filters can be chained in one stream
+--EXTENSIONS--
+filter
+--FILE--
+<?php
+
+function createFilterChains($n, $resource) {
+    $filter = 'string.toupper';
+    $pipes = 'php://filter/' . implode('|', array_fill(0, $n, $filter)) . "/resource=$resource";
+    $slashes = 'php://filter/' . implode('/', array_fill(0, $n, $filter)) . "/resource=$resource";
+    $resources = str_repeat("php://filter/$filter/resource=", $n) . $resource;
+    return [$pipes, $slashes, $resources];
+}
+
+echo "# file_get_contents on 16 filters\n";
+$allowed_read = createFilterChains(16, 'data:text/plain,sixteen');
+foreach ($allowed_read as $chain) {
+    var_dump(file_get_contents($chain));
+}
+
+echo "# include on 16 filters\n";
+$allowed_include = createFilterChains(16, 'php://temp');
+foreach ($allowed_include as $chain) {
+    var_dump(include $chain);
+}
+
+echo "# file_get_contents on 17 filters\n";
+$blocked_read = createFilterChains(17, 'data:text/plain,seventeen');
+foreach ($blocked_read as $chain) {
+    var_dump(file_get_contents($chain));
+}
+
+echo "# include on 17 filters\n";
+$blocked_include = createFilterChains(17, 'php://temp');
+foreach ($blocked_include as $chain) {
+    var_dump(include $chain);
+}
+
+echo "# file_get_contents on 3 filters, max_filter_count=2\n";
+$ctx = stream_context_create(['filter' => ['max_filter_count' => 2]]);
+$blocked_read = createFilterChains(3, 'data:text/plain,three');
+foreach ($blocked_read as $chain) {
+    var_dump(file_get_contents($chain, false, $ctx));
+}
+
+echo "# file_get_contents on 19 filters, max_filter_count=20\n";
+$ctx = stream_context_create(['filter' => ['max_filter_count' => 20]]);
+$allowed_read = createFilterChains(19, 'data:text/plain,nineteen');
+foreach ($allowed_read as $chain) {
+    var_dump(file_get_contents($chain, false, $ctx));
+}
+
+echo "# warning is only given once, even when we add two filters over the limit\n";
+$blocked_read = createFilterChains(18, 'data:text/plain,eighteen');
+foreach ($blocked_read as $chain) {
+    var_dump(file_get_contents($chain));
+}
+
+echo "# warn on too many write filters, even when number of read filters is OK\n";
+$filter = 'string.toupper';
+$write_filters = implode('|', array_fill(0, 16, $filter));
+$fp = fopen("php://filter/write=$write_filters/$filter/resource=php://temp", 'w+');
+var_dump(is_resource($fp));
+
+echo "# setting max_filter_count to -1 disables warning\n";
+$ctx = stream_context_create(['filter' => ['max_filter_count' => -1]]);
+$allowed_read = createFilterChains(20, 'data:text/plain,twenty');
+foreach ($allowed_read as $chain) {
+    var_dump(file_get_contents($chain, false, $ctx));
+}
+
+echo "# many filters with stream_filter_append still works\n";
+$fp = fopen('data:text/plain,stream_filter_append', 'r');
+for ($i = 0; $i < 80; $i++) {
+    stream_filter_append($fp, 'string.toupper');
+}
+var_dump(fread($fp, 30));
+fclose($fp);
+
+?>
+--EXPECTF--
+# file_get_contents on 16 filters
+string(7) "SIXTEEN"
+string(7) "SIXTEEN"
+string(7) "SIXTEEN"
+# include on 16 filters
+int(1)
+int(1)
+int(1)
+# file_get_contents on 17 filters
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+string(9) "SEVENTEEN"
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+string(9) "SEVENTEEN"
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+string(9) "SEVENTEEN"
+# include on 17 filters
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+int(1)
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+int(1)
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+int(1)
+# file_get_contents on 3 filters, max_filter_count=2
+
+Warning: file_get_contents(): Failed to open stream: too many filters in %s on line %d
+bool(false)
+
+Warning: file_get_contents(): Failed to open stream: too many filters in %s on line %d
+bool(false)
+
+Warning: file_get_contents(): Failed to open stream: too many filters in %s on line %d
+bool(false)
+# file_get_contents on 19 filters, max_filter_count=20
+string(8) "NINETEEN"
+string(8) "NINETEEN"
+string(8) "NINETEEN"
+# warning is only given once, even when we add two filters over the limit
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+string(8) "EIGHTEEN"
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+string(8) "EIGHTEEN"
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+string(8) "EIGHTEEN"
+# warn on too many write filters, even when number of read filters is OK
+
+Deprecated: Using more than 16 filters in a php://filter URL is deprecated, set this limit using the stream context option max_filter_count, or use stream_filter_append in %smax_filter_chain.php on line %d
+bool(true)
+# setting max_filter_count to -1 disables warning
+string(6) "TWENTY"
+string(6) "TWENTY"
+string(6) "TWENTY"
+# many filters with stream_filter_append still works
+string(20) "STREAM_FILTER_APPEND"

main/streams/filter.c

@@ -339,6 +339,7 @@ PHPAPI void php_stream_filter_prepend_ex(php_stream_filter_chain *chain, php_str
 		chain->tail = filter;
 	}
 	chain->head = filter;
+	chain->num_filters += 1;
 	filter->chain = chain;
 }
 
@@ -359,6 +360,7 @@ PHPAPI zend_result php_stream_filter_append_ex(php_stream_filter_chain *chain, p
 		chain->head = filter;
 	}
 	chain->tail = filter;
+	chain->num_filters += 1;
 	filter->chain = chain;
 
 	if (&(stream->readfilters) == chain && (stream->writepos - stream->readpos) > 0) {
@@ -444,6 +446,7 @@ PHPAPI void php_stream_filter_append(php_stream_filter_chain *chain, php_stream_
 			filter->prev->next = NULL;
 			chain->tail = filter->prev;
 		}
+		chain->num_filters -= 1;
 	}
 }
 
@@ -545,6 +548,8 @@ PHPAPI php_stream_filter *php_stream_filter_remove(php_stream_filter *filter, bo
 		filter->chain->tail = filter->prev;
 	}
 
+	filter->chain->num_filters -= 1;
+
 	if (filter->res) {
 		zend_list_delete(filter->res);
 	}

main/streams/php_stream_filter_api.h

@@ -108,6 +108,7 @@ typedef struct _php_stream_filter_ops {
 
 typedef struct _php_stream_filter_chain {
 	php_stream_filter *head, *tail;
+	zend_long num_filters;
 
 	/* Owning stream */
 	php_stream *stream;