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From "Plüm, Rüdiger, VF-Group" <ruediger.pl...@vodafone.com>
Subject RE: svn commit: r1161661 - /httpd/httpd/trunk/modules/http/byterange_filter.c
Date Fri, 26 Aug 2011 14:34:25 GMT
 

> -----Original Message-----
> From: Jim Jagielski [mailto:jim@apache.org] 
> Sent: Freitag, 26. August 2011 16:27
> To: dev@httpd.apache.org
> Subject: Re: svn commit: r1161661 - 
> /httpd/httpd/trunk/modules/http/byterange_filter.c
> 
> > 
> > I guess we can do both: Count the ',' and give the number 
> to apr_array_make
> > 
> 
> Doesn't that mean that someone can craft a nasty Range (e.g: 
> 0-0,1-1,2-2,
> 3-3,....99999999-99999999 and cause us to preallocate a bunch
> of memory when at the end we'll get 0-99999999 ???

In principal yes. Two things can happen:

1. The ranges are valid and do not overlap or are not mergable. In this
   case we need to allocate that memory anyway.

2. The ranges are mergable. In this case we allocate too much memory
   for the array. But this effect is limited by the maximum length a header field can
   have. And if this is not enough do a sane cut for the preallocation:

   MIN(number of ranges, MAX_PREALLOCATED_ARRAY_MEMBERS)

This should work fine for the typical use case where we can't merge anything
and avoid running in a DoS trap if we have a large number of mergable ranges.


Regards

Rüdiger 

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