Re: [Caml-list] Re: [oss-security] CVE request: Hash DoS vulnerability (ocert-2011-003)

[Alain Frisch <alain@frisch.fr>]

On 03/13/2012 07:27 PM, David Allsopp wrote:
> +1. Surely in projects where repeatability is important, the change in behaviour to randomly seeded tables would be quickly noticed

The problem is that the randomization might go unnoticed if the 
high-level outputs of the program does not depend on the ordering when 
enumerating the hash table (because the "interesting" algorithms built 
above the hash table is supposed to be invariant w.r.t. the ordering of 
their input).  So the programmer doesn't turn randomization off, but one 
day, the end-user discovers a bug (caused by a very subtle bug in the 
algorithm, which in fact, depends on the ordering), and one cannot 
reproduce it.

Ocsigen and other web libraries can decide to turn randomization on by 
default to protect their users, but for a general purpose programming 
system like OCaml's stdlib, increasing reproducibility seems more 
important than protecting programmers from high-level defects 
(possibility of DoS) caused by a poor choice or use of low-level data 
structure.


Alain