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SubjectRe: Shared memory usage
Did you think about getting shared memory information using
shmctl(IPC_STAT). It provides useful information but I am not sure if
that will serve your purpose fully.

Ram Gupta

On 1/16/06, linux-os (Dick Johnson) <> wrote:
> On Mon, 16 Jan 2006 wrote:
> > On Mon, 16 Jan 2006 09:15:16 EST, "linux-os (Dick Johnson)" said:
> >> But the customer complained during certification testing
> >> that shared memory in use is not measured and therefore
> >> cannot be verified. This means that there may be rogue
> >> communications channels, using shared memory, in the
> >> system. I need to prove that there are no such channels
> >> by metering the shared memory and then accounting for
> >> every bit shown.
> >
> > The customer is confused, and your test is broken as designed.
> >
> > The fact that you look in /proc/meminfo and account for every shared
> > memory page *at this instant* doesn't mean there isn't a communication
> > channel *at some other time*. Even if you run a daemon that does nothing
> > but monitor this usage 10 times a second, and complain if a discrepancy
> > is found, it *still* won't work:
> >
> > 1) It's racy - 2 processes can mmap() some space during that 0.1 seconds,
> > transfer the info, and detach the memory without your knowledge.
> >
> > 2) It's racy - if you inquire *while* some other process is in some
> > intermediate
> > state, causing false positives that will drive the SSO nuts.
> >
> > The *proper* solution is to use something like SELinux that will flat-out
> > *prohibit* the attachment of a shared memory segment that isn't permitted.
> >
> The customer is not confused and is, in fact, a known expert.
> This is not a "general purpose" setup. There are no executables
> except what is burned into R/O PROM. There is no code that can
> upload new executables nor any way to execute them. There is no
> shell and no init.
> There is a startup program called 'init' for convenience, but
> whatever it does is hard-coded. It starts a bunch of predefined
> tasks and sleeps after performing some initialization.
> So, if the executable files are exactly like those which
> were reviewed during a security review, and if all
> communications between processes can be accounted for,
> including shared memory, then it can be guaranteed that
> whatever is being executed is exactly what passed the
> security review. However, if all communications channels
> cannot be accounted for, then it is not possible for such
> a guarantee.
> It can be argued that, once the executable code is known,
> there is no reason to review possible rogue communications
> channels. However, the customer is an expert in this field
> and requires an audit of all possible communications
> channels, including shared memory.
> Note that this is an audit. The code for every communications
> channel is reviewed. To verify that all such channels are
> audited, one needs to find them. For instance even 'vdso' is
> audited. These are not continuous audits that operate at
> run-time. The reason for this 'static' audit is so that
> CPU time eating checks don't have to be done at runtime.
> Cheers,
> Dick Johnson
> Penguin : Linux version on an i686 machine (5589.54 BogoMips).
> Warning : 98.36% of all statistics are fiction.
> .
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> Thank you.
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