In legacy text conversion filters, reset filter state in 'flush' function

Up until now, I believed that mbstring had been designed such
that (legacy) text conversion filter objects should not be
re-used after the 'flush' function is called to complete a
text conversion operation.

However, it turns out that the implementation of
_php_mb_encoding_handler_ex DID re-use filter objects
after flush. That means that functions which were based on
_php_mb_encoding_handler_ex, including mb_parse_str and
php_mb_post_handler, would break in some cases; state left
over from converting one substring (perhaps a variable name)
would affect the results of converting another substring
(perhaps the value of the same variable), and could cause
extraneous characters to get inserted into the output.

All this code should be deleted soon, but fixing it helps me
to avoid spurious failures when fuzzing the new/old code to
look for differences in behavior.

(This bug fix commit was originally applied to PHP-8.2 when fuzzing
the new mbstring text conversion code to check for differences with
the old code. Later, Kentaro Ohkouchi kindly reported a problem with
mb_encode_mimeheader under PHP 8.1 which was caused by the same issue.
Hence, this commit was backported to PHP-8.1.)

Fixes GH-9683.

Author: alexdowad

ext/mbstring/libmbfl/filters/mbfilter_big5.c

@@ -251,6 +251,7 @@ static int mbfl_filt_conv_big5_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status == 1) {
 		/* 2-byte character was truncated */
+		filter->status = 0;
 		CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
 	}
 

ext/mbstring/libmbfl/filters/mbfilter_cp5022x.c

@@ -312,6 +312,7 @@ static int mbfl_filt_conv_cp5022x_wchar_flush(mbfl_convert_filter *filter)
 		/* 2-byte (JIS X 0208 or 0212) character was truncated */
 		CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
 	}
+	filter->status = 0;
 
 	if (filter->flush_function) {
 		(*filter->flush_function)(filter->data);
@@ -650,7 +651,7 @@ mbfl_filt_conv_wchar_cp50222_flush(mbfl_convert_filter *filter)
 		CK((*filter->output_function)(0x28, filter->data));		/* '(' */
 		CK((*filter->output_function)(0x42, filter->data));		/* 'B' */
 	}
-	filter->status &= 0xff;
+	filter->status = 0;
 
 	if (filter->flush_function) {
 		(*filter->flush_function)(filter->data);

ext/mbstring/libmbfl/filters/mbfilter_cp51932.c

@@ -176,6 +176,7 @@ static int mbfl_filt_conv_cp51932_wchar_flush(mbfl_convert_filter *filter)
 	if (filter->status) {
 		/* Input string was truncated */
 		(*filter->output_function)(MBFL_BAD_INPUT, filter->data);
+		filter->status = 0;
 	}
 
 	if (filter->flush_function) {

ext/mbstring/libmbfl/filters/mbfilter_cp932.c

@@ -272,6 +272,7 @@ static int mbfl_filt_conv_cp932_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status) {
 		(*filter->output_function)(MBFL_BAD_INPUT, filter->data);
+		filter->status = 0;
 	}
 
 	if (filter->flush_function) {

ext/mbstring/libmbfl/filters/mbfilter_cp936.c

@@ -169,6 +169,7 @@ static int mbfl_filt_conv_cp936_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status) {
 		/* 2-byte character was truncated */
+		filter->status = 0;
 		CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
 	}
 

ext/mbstring/libmbfl/filters/mbfilter_euc_cn.c

@@ -210,6 +210,7 @@ static int mbfl_filt_conv_euccn_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status == 1) {
 		/* 2-byte character was truncated */
+		filter->status = 0;
 		CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
 	}
 

ext/mbstring/libmbfl/filters/mbfilter_euc_jp.c

@@ -178,6 +178,7 @@ static int mbfl_filt_conv_eucjp_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status) {
 		(*filter->output_function)(MBFL_BAD_INPUT, filter->data);
+		filter->status = 0;
 	}
 
 	if (filter->flush_function) {

ext/mbstring/libmbfl/filters/mbfilter_euc_jp_win.c

@@ -223,6 +223,7 @@ static int mbfl_filt_conv_eucjpwin_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status) {
 		(*filter->output_function)(MBFL_BAD_INPUT, filter->data);
+		filter->status = 0;
 	}
 
 	if (filter->flush_function) {

ext/mbstring/libmbfl/filters/mbfilter_euc_kr.c

@@ -197,6 +197,7 @@ static int mbfl_filt_conv_euckr_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status == 1) {
 		/* 2-byte character was truncated */
+		filter->status = 0;
 		CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
 	}
 

ext/mbstring/libmbfl/filters/mbfilter_euc_tw.c

@@ -243,6 +243,7 @@ static int mbfl_filt_conv_euctw_wchar_flush(mbfl_convert_filter *filter)
 {
 	if (filter->status) {
 		/* 2-byte or 4-byte character was truncated */
+		filter->status = 0;
 		CK((*filter->output_function)(MBFL_BAD_INPUT, filter->data));
 	}