Fix #80384: limit read buffer size

In the case of a stream with no filters, php_stream_fill_read_buffer
only reads stream->chunk_size into the read buffer. If the stream has
filters attached, it could unnecessarily buffer a large amount of data.

With this change, php_stream_fill_read_buffer only proceeds until either
the requested size or stream->chunk_size is available in the read buffer.

Co-authored-by: Christoph M. Becker <cmbecker69@gmx.de>

Closes GH-6444.

NEWS

@@ -4,6 +4,8 @@ PHP                                                                        NEWS
 
 - Core:
   . Fixed bug #80523 (bogus parse error on >4GB source code). (Nikita)
+  . Fixed bug #80384 (filter buffers entire read until file closed). (Adam
+    Seitz, cmb)
 
 - Date:
   . Fixed bug #80376 (last day of the month causes runway cpu usage. (Derick)

ext/standard/tests/streams/bug79984.phpt

@@ -52,6 +52,6 @@ fclose($f2);
 --EXPECT--
 filter onCreate
 filtered 8192 bytes.
-filtered 128 bytes and closing.
+filtered 128 bytes and closing. Stream has reached end-of-file.
 int(8320)
 filter onClose

main/streams/streams.c

@@ -542,6 +542,7 @@ PHPAPI int _php_stream_fill_read_buffer(php_stream *stream, size_t size)
 	/* allocate/fill the buffer */
 
 	if (stream->readfilters.head) {
+		size_t to_read_now = MIN(size, stream->chunk_size);
 		char *chunk_buf;
 		php_stream_bucket_brigade brig_in = { NULL, NULL }, brig_out = { NULL, NULL };
 		php_stream_bucket_brigade *brig_inp = &brig_in, *brig_outp = &brig_out, *brig_swap;
@@ -549,7 +550,7 @@ PHPAPI int _php_stream_fill_read_buffer(php_stream *stream, size_t size)
 		/* allocate a buffer for reading chunks */
 		chunk_buf = emalloc(stream->chunk_size);
 
-		while (!stream->eof && (stream->writepos - stream->readpos < (zend_off_t)size)) {
+		while (!stream->eof && (stream->writepos - stream->readpos < (zend_off_t)to_read_now)) {
 			ssize_t justread = 0;
 			int flags;
 			php_stream_bucket *bucket;

tests/basic/bug80384.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Bug #80384 large reads cause filters to internally buffer large amounts of memory
+--FILE--
+<?php
+/* First, create a file to read */
+$tmp_filename = __DIR__ . "/bug80384.tmp";
+$fp = fopen($tmp_filename, 'w');
+for ($i=0; $i<1024; $i++) {
+    fwrite($fp, str_repeat('ABCDEFGH', 1024));
+}
+fclose($fp);
+
+/* Stream the file through a filter */
+$fp = fopen($tmp_filename, 'r');
+$filter = stream_filter_append($fp, "string.rot13");
+
+$mem_start = memory_get_usage();
+fread($fp, 8 * 1024 * 1024);
+$mem_final = memory_get_usage();
+fclose($fp);
+var_dump($mem_final - $mem_start < 32768);
+?>
+--CLEAN--
+<?php
+unlink(__DIR__ . "/bug80384.tmp");
+?>
+--EXPECT--
+bool(true)