Re: [PHP-DEV] [PATCH] Fix for php://input returning duplicate data in some cases

[Jani Taskinen]

    Are there any bug reports about this at bugs.php.net ?
    If not, enter one and put the patch online somewhere were
    we can download it as text file. (and the url to that into
    the bug report)

    Does this problem exist with PHP_4_3 branch?

    --Jani

On Wed, 16 Mar 2005, Jozef Hatala wrote:

In some cases, the php://input stream returns incorrect data.
This was discovered as a data corruption when directly parsing
a POSTed XML with a long text-node.

The problem is between main/streams/streams.c and
ext/standard/php_fopen_wrapper.c.

The XML parser requests data from the stream in 4000 byte
chunks.

_php_stream_read requests data from the handler for php://input
in 8192 byte chunks.  It uses two counters stream->readpos
and stream->writepos to handle the buffering.  Just before
returning the next 4000 byte chunk, _php_stream_read advances
the stream->position.

The handler for php://input in php_stream_input_read
uses stream->position to address the contents of
SG(request_info).raw_post_data and serves a 8192 byte chunk
starting at that position.

The problem shows itself on the third call of _php_stream_read.
In the first iteration of the while(size>0) loop, it uses the
192 bytes left over in the buffer.  In the second iteration it
needs to refill to buffer, so it calls php_stream_input_read.
But stream->position has not been advanced by 192 yet, so
php_stream_input_read ends up returning a buffer starting with
the same 192 bytes.

The patch consists in simply updating stream->position
immediately, instead of accumulating didread and only updating
stream->position at the end.  This way php_stream_input_read
always sees an accurate value of the stream->position.

Here it is.  It is made against php-5.0.3, but it also applies
to php5-200503161930.

==== begin ====
diff -ru php-5.0.3.orig/main/streams/streams.c php-5.0.3/main/streams/streams.c
--- php-5.0.3.orig/main/streams/streams.c       2004-11-15 15:44:14.000000000 
-0800
+++ php-5.0.3/main/streams/streams.c    2005-03-16 13:08:02.000000000 -0800
@@ -560,6 +560,7 @@
                        size -= toread;
                        buf += toread;
                        didread += toread;
+                       stream->position += toread;
                }

                /* ignore eof here; the underlying state might have changed */
@@ -584,6 +585,7 @@
                }
                if (toread > 0) {
                        didread += toread;
+                       stream->position += toread;
                        buf += toread;
                        size -= toread;
                } else {
@@ -596,10 +598,6 @@
                        break;
        }

-       if (didread > 0) {
-               stream->position += didread;
-       }
-
        return didread;
}

==== end ====

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