Bug #69487 [Ana]: SAPI may truncate POST data
Edit report at https://bugs.php.net/bug.php?id=69487&edit=1
ID: 69487
Updated by: mike@php.net
Reported by: erik at datahack dot se
Summary: SAPI may truncate POST data
Status: Analyzed
Type: Bug
Package: *Web Server problem
Operating System: *
PHP Version: PHP 5.6.12RC1
Assigned To: cmb
Block user comment: N
Private report: N
New Comment:
-1 on E_ERROR
I'd rather suggest clearing the input stream an generating an E_WARNING to inform the system
administrator.
Previous Comments:
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[2015-08-04 21:24:14] cmb@php.net
Indeed, such data loss would be a bad thing. Of course, we should
check whether the read_bytes are actually written by
php_stream_write()[1]. What to do otherwise might be not so
obvious, but the simplest solution would be to bail out with
E_ERROR. As this error condition is supposed to be *very* rare,
the simple handling seems to be appropriate.
[1] <https://github.com/php/php-src/blob/php-7.0.0beta2/main/SAPI.c#L288>
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[2015-04-20 10:21:46] erik at datahack dot se
Description:
------------
If the SAPI fails to write the POST data to disk (eg. due to file system full or tmp folder is
non-writable for other reasons), The PHP interpreter will get an incomplete/truncated POST request.
This is very bad for data consistency if data is lost upon POST.
One workaround in the PHP script would be to check the content-length against the length of
php://input.
if (count($_POST) &&
(int)$_SERVER['CONTENT_LENGTH'] != strlen(file_get_contents("php://input")))
...
display_startup_errors triggers only a warning if the file can't be created (but the data is
still corrupted). There are two cases that can happen and shouldn't result in corrupt data.
1. Temp file cannot be created
2. Data cannot be written to temp file
https://github.com/php/php-src/blob/master/main/SAPI.c#L288
Test script:
---------------
If sys_temp_dir can't be written to this will cause corrupt data.
<?php
if (count($_POST)) {
echo strlen(file_get_contents("php://input"))."<br>";
echo file_get_contents("php://input")."<br>";
}
?>
<form method="post">
<input type="hidden" name="data" value="<?php echo
str_repeat("x", 16384).str_repeat("y", 16384).str_repeat("z", 16384);
?>">
<input type="submit">
</form>
Expected result:
----------------
No POST data or an internal error would be better than just continue with corrupt data...
Actual result:
--------------
PHP continues to process the request with corrupt data.
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Edit this bug report at https://bugs.php.net/bug.php?id=69487&edit=1
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