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Date:      Mon, 25 Apr 2011 17:46:33 +0200
From:      "C. P. Ghost" <cpghost@cordula.ws>
To:        freebsd-questions@freebsd.org
Subject:   Re: Password theft from memory?
Message-ID:  <BANLkTinvvWhEy_A5ao=XWTpQOSTX0Vm2_A@mail.gmail.com>
In-Reply-To: <20110425151536.GA61425@stainmore>
References:  <BANLkTimJWAxW_4OmoeBQrvDDLjD-5Vr5hQ@mail.gmail.com> <BANLkTin_S%2BBRWu79AH16tPdgZd%2BUgZQAzQ@mail.gmail.com> <20110425151846.0a5359fd@gumby.homeunix.com> <20110425151536.GA61425@stainmore>

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On Mon, Apr 25, 2011 at 5:15 PM, Bob Hall <rjhjr0@gmail.com> wrote:
> On Mon, Apr 25, 2011 at 03:18:46PM +0100, RW wrote:
>> I don't believe the heap is allocated zeroed pages. =A0The kernel
>> does allocate such pages to the BSS segment, but that's because it
>> holds zeroed data such as C static variables.
>
> According to McKusick and Neville-Neil's book on FreeBSD, sbrk extends
> the uninitialized data segment with zero-filled pages. Since malloc() is
> an interface to sbrk, it does the same thing.

True, except that malloc(3) now uses both sbrk(2) and mmap(2) allocators,
depending on the user-settable flags in /etc/malloc.conf, MALLOC_OPTIONS
and the global variable _malloc_options. So you have to look into mmap(2)
too.

-cpghost.

--=20
Cordula's Web. http://www.cordula.ws/



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