Re: Zeroed pages returned for heap

From: Nagendra Singh Tomar (nagendra_tomar_at_adaptec.com)
Date: 06/08/05

  • Next message: Grant Grundler: "Re: [Fastboot] Re: [RFC/PATCH] Kdump: Disabling PCI interrupts in capture kernel" 
    Date:	Wed, 8 Jun 2005 09:38:05 +0530 (IST)
To: Peter Staubach <staubach@redhat.com>

    On Tue, 7 Jun 2005, Peter Staubach wrote:

    > Nagendra Singh Tomar wrote:
    >
    > >Hi all,
    > > The short version first.
    > >Is it OK for an application (a C library implementing malloc/calloc is
    > >also an application) to assume that the pages returned by the OS for heap
    > >allocation (either directly thru brk() or thru mmap(MAP_ANONYMOUS)) will
    > >be zero filled.
    > >
    >
    > An application which makes assumptions about the contents of newly allocated
    > memory would seem to be making very dangerous assumptions.

    Thats what glibc does. Ulrich confirmed that. I would say thats not a bad
    optimization on glibc's part as it does not really make sense to zero out
    a memory again in user space if we know for sure that new heap memory that
    kernel hands over to us will be zeroed. I'm not sure though whether this
    is a documented kernel ABI.

    >
    > Ignoring that, would it not be considered to be a security violation to hand
    > pieces of memory to applications without erasing the old contents of the
    > pages?

    I understand that for a desktop/server running Linux but not for an
    embedded box where all the applications that run on the box is controlled
    by you.

    Thanx,
    Tomar

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  • Next message: Grant Grundler: "Re: [Fastboot] Re: [RFC/PATCH] Kdump: Disabling PCI interrupts in capture kernel"

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