Fix #81294: Segfault when removing a filter

We need to call the proper method.

Closes GH-7308.

Author: cmb69

NEWS

@@ -22,6 +22,9 @@ PHP                                                                        NEWS
     (George Dietrich)
   . Fixed bug #74960 (Heap buffer overflow via str_repeat). (cmb, Dmitry)
 
+- Streams:
+  . Fixed bug #81294 (Segfault when removing a filter). (cmb)
+
 29 Jul 2021, PHP 7.4.22
 
 - Core:

ext/standard/tests/filters/bug81294.phpt

@@ -0,0 +1,24 @@
+--TEST--
+Bug #81294 (Segfault when removing a filter)
+--SKIPIF--
+<?php
+if (!extension_loaded('zlib')) die("skip zlib extension not available");
+?>
+--FILE--
+<?php
+$f = fopen(__DIR__ . "/bug81294.txt", "wb+");
+$flt1 = stream_filter_append($f, "zlib.deflate", STREAM_FILTER_WRITE);
+$flt2 = stream_filter_append($f, "string.rot13", STREAM_FILTER_WRITE);
+fwrite($f, "test");
+stream_filter_remove($flt1);
+fwrite($f, "test");
+stream_filter_remove($flt2);
+rewind($f);
+var_dump(urlencode(fread($f, 1024)));
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/bug81294.txt");
+?>
+--EXPECT--
+string(16) "%2BV-.%01%00grfg"

main/streams/filter.c

@@ -418,7 +418,7 @@ PHPAPI int _php_stream_filter_flush(php_stream_filter *filter, int finish)
 	for(current = filter; current; current = current->next) {
 		php_stream_filter_status_t status;
 
-		status = filter->fops->filter(stream, current, inp, outp, NULL, flags);
+		status = current->fops->filter(stream, current, inp, outp, NULL, flags);
 		if (status == PSFS_FEED_ME) {
 			/* We've flushed the data far enough */
 			return SUCCESS;