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Bug #40754 substr() checks overflow
Submitted: 2007-03-08 00:57 UTC Modified: 2007-09-06 19:22 UTC
From: christopher dot jones at oracle dot com Assigned:
Status: Closed Package: Strings related
PHP Version: 5CVS-2007-03-08 (CVS) OS: Enterprise Linux
Private report: No CVE-ID:
 [2007-03-08 00:57 UTC] christopher dot jones at oracle dot com
Description:
------------
Related to the problems fixes in today's patches for substr_count() and substr_compare() there are issues with substr() and substr_replace().
Also there might be return value inconsistencies with strspn() and strcspn().

Reproduce code:
---------------
<?php

$v = 2147483647;  # INT_MAX on 32bit Linux

# Tries to allocate too much memory
var_dump(substr("abcde", 1, $v));
var_dump(substr_replace("abcde", "x", $v, $v));

# Functions with ill-defined behavior
var_dump(strspn("abcde", "abc", $v, $v)); # should return 0 but gives false
var_dump(strcspn("abcde", "abc", $v, $v)); # should return 0 but gives false

# Crashes
var_dump(substr_count("abcde", "abc", $v, $v));    # crashes <= 5.2.1. Fixed by Ilia http://news.php.net/php.cvs/43456
var_dump(substr_compare("abcde", "abc", $v, $v));  # crashes <= 5.2.1. Fixed by Stanislav http://news.php.net/php.cvs/43453

# Other tests (currently working)
var_dump(stripos("abcde", "abc", $v));
var_dump(substr_count("abcde", "abc", $v, 1));
var_dump(substr_count("abcde", "abc", 1, $v));
var_dump(strpos("abcde", "abc", $v));
var_dump(stripos("abcde", "abc", $v));
var_dump(strrpos("abcde", "abc", $v));
var_dump(strripos("abcde", "abc", $v));
var_dump(strncmp("abcde", "abc", $v));
var_dump(chunk_split("abcde", $v, "abc"));
var_dump(substr("abcde", $v, $v));
var_dump(str_repeat("a", $v+1));

?>



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 [2007-03-09 01:01 UTC] christopher dot jones at oracle dot com
I've sent a patch and testcase to Tony.
 [2007-03-09 02:00 UTC] iliaa@php.net
This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.

The strspn() and strcspn() is expected behavior. 
 [2007-09-06 19:22 UTC] chagenbu@php.net
It took me a while to track this down, but this change to substr is breaking a lot of previously working code.

I don't know if substr was previously documented to return false if you asked for more characters than were in the string, but returning the whole string for a negative length, and an empty string for a positive offset, was *much* more useful than false. Returning false means we need to do a lot more checking for length of string, or casting, and really just makes this a pain.

It's not just me:
http://us.php.net/manual/en/function.substr.php#75999

Can we revert the changes to substr please?
 
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