arc4random weakness

[Konstantin Belousov]

On Thu, Mar 16, 2017 at 01:48:45PM +0100, Dag-Erling Sm??rgrav wrote:
> Andrey Chernov <ache at freebsd.org> writes:
> > Steven Chamberlain <steven at pyro.eu.org> writes:
> > > Also it is great to see INHERIT_ZERO was added to mmap(2)!
> > It is not so great. For a program which forks very often zeroing even
> > one page will be slowdown.
> 
> Wouldn't it be possible to just set up the page entry but leave it
> unmapped, so that it is paged in (and zeroed if necessary) on first
> access?  Thus, a process that uses arc4random() and fork()s would not
> incur a penalty until (and unless) the child uses arc4random() too.
This is how the forking code works, without any additional coding,
for the INHERIT_ZERO regions as well.

> 
> > It will be better and faster to implement it as fork syscall wrapper
> > setting single variable, as it already done for threaded lib.
> 
> fork() and vfork() and pdfork() and...  From a security point of view, I
> prefer to have it in a single place.
> 
> DES
> -- 
> Dag-Erling Sm??rgrav - des at des.no
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