Date: Mon, 25 Apr 2011 13:54:20 -0400 From: Bob Hall <rjhjr0@gmail.com> To: "C. P. Ghost" <cpghost@cordula.ws> Cc: freebsd-questions@freebsd.org Subject: Re: Password theft from memory? Message-ID: <20110425175420.GA61811@stainmore> In-Reply-To: <BANLkTinvvWhEy_A5ao=XWTpQOSTX0Vm2_A@mail.gmail.com> References: <BANLkTimJWAxW_4OmoeBQrvDDLjD-5Vr5hQ@mail.gmail.com> <BANLkTin_S%2BBRWu79AH16tPdgZd%2BUgZQAzQ@mail.gmail.com> <20110425151846.0a5359fd@gumby.homeunix.com> <20110425151536.GA61425@stainmore> <BANLkTinvvWhEy_A5ao=XWTpQOSTX0Vm2_A@mail.gmail.com>
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On Mon, Apr 25, 2011 at 05:46:33PM +0200, C. P. Ghost wrote: > 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. The 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. Good point. From the man page: "Any such extension beyond the end of the mapped object will be zero-filled." and "A successful mmap deletes any previous mapping in the allocated address range."
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