linux-kernel - Re: [PATCH] Undo some of the pseudo-security madness

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Date:	Wed, 31 Jan 2007 17:59:48 +0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Samium Gromoff <_deepfire@...lingofgreen.ru>
Cc:	Pavel Machek <pavel@....cz>, Valdis.Kletnieks@...edu,
	David Wagner <daw@...berkeley.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Undo some of the pseudo-security madness

> No amount of carefulness will prevent vendors stick arbitrarily
> damaging values of stack and mmap base randomisation, severely reducing
> the usefullness of MAP_FIXED.

MAP_FIXED is useful still. The only safe way is to use addresses you got
from mmap(), eg you overmap something.
Anything else is madness, with or without randomization. The C library
for example is free, and does, allocate memory and stacks etc etc.

Same for many other libraries; in addition libraries change in size all
the time... MAP_FIXED of an address you don't KNOW is free is a bug.
Period.
(using an address previously obtained from mmap() is safest, but you
could in theory also parse /proc/self/maps, although that is racey,
since nothing guarantees that the C library didn't spawn a background
thread that allocates memory)

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