Fix #81092: fflush before stream_filter_remove corrupts stream

When doing a non finishing flush, BZ2_bzCompress() returns BZ_FLUSH_OK
(not BZ_FINISH_OK) what requires us to do further flushes right away.

We also refactor the while-loop as do-loop.

Closes GH-7113.

NEWS

@@ -10,6 +10,10 @@ PHP                                                                        NEWS
   . Fixed bug #81070 (Integer underflow in memory limit comparison).
     (Peter van Dommelen)
 
+- Bzip2:
+  . Fixed bug #81092 (fflush before stream_filter_remove corrupts stream).
+    (cmb)
+
 - OpenSSL:
   . Fixed bug #76694 (native Windows cert verification uses CN as sever name).
     (cmb)

ext/bz2/bz2_filter.c

@@ -268,8 +268,7 @@ static php_stream_filter_status_t php_bz2_compress_filter(
 
 	if (flags & PSFS_FLAG_FLUSH_CLOSE || ((flags & PSFS_FLAG_FLUSH_INC) && !data->is_flushed)) {
 		/* Spit it out! */
-		status = BZ_FINISH_OK;
-		while (status == BZ_FINISH_OK) {
+		do  {
 			status = BZ2_bzCompress(&(data->strm), (flags & PSFS_FLAG_FLUSH_CLOSE ? BZ_FINISH : BZ_FLUSH));
 			data->is_flushed = 1;
 			if (data->strm.avail_out < data->outbuf_len) {
@@ -281,7 +280,7 @@ static php_stream_filter_status_t php_bz2_compress_filter(
 				data->strm.next_out = data->outbuf;
 				exit_status = PSFS_PASS_ON;
 			}
-		}
+		} while (status == (flags & PSFS_FLAG_FLUSH_CLOSE ? BZ_FINISH_OK : BZ_FLUSH_OK));
 	}
 
 	if (bytes_consumed) {

ext/bz2/tests/bug81092.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Bug #81092 (fflush before stream_filter_remove corrupts stream)
+--SKIPIF--
+<?php
+if (!extension_loaded('bz2')) die('skip bz2 extension not available');
+?>
+--FILE--
+<?php
+$stream = fopen(__DIR__ . "/81092.bz2", 'wb+');
+$filter = stream_filter_append($stream, 'bzip2.compress', STREAM_FILTER_WRITE, ['blocks' => 9, 'work' => 0]);
+fwrite($stream, random_bytes(8192));
+fflush($stream);
+stream_filter_remove($filter);
+
+var_dump(strlen(bzdecompress(file_get_contents(__DIR__ . "/81092.bz2"))));
+?>
+--CLEAN--
+<?php
+@unlink(__DIR__ . "/81092.bz2");
+?>
+--EXPECT--
+int(8192)