Harlan Stenn wrote:
I see to points Damion has raised where I do not see your response.
The first is that there exist several libraries where the C library provides
the nano calls but implements them using the (older) microsecond
calls. Therefore there is no data available below the microsecond and our
code is not handling this case.
Damion, what does clock_getres() return on these systems?
I've justed tested it on a few different linux systems here (SH, ARM, x86 and
MIPS)
and linux 2.4.x kernels always return 10ms, and linux 2.6.0 kernels always
return 1ms.
Looking at the source, it would seem this is always going to be wrong - it just
returns the clock tick frequency (100Hz for 2.4 kernel and 1000Hz for 2.6 kernel)
the system clock precision is calculated in default_get_precision()
in ntp_proto.c - this function uses consecutive calls to
get_systime() to calculate the minimum tick difference. Won't this
be always wrong if the random fuzz code in get_systime() is used,
and give a much higher precision than is really available?
This could easily be fixed by adding another parameter to get_systime() that
would disable the fuzz, assuming it really is a problem (from my initial
glance I think it is a problem, but I am working on way too many things
right now).
That could work.
If get_systime() only optionally added fuzz, then it can still be used to calculate
the real precision when called from default_get_precision().
That sys_precision value can then be used on subsequent calls to get_systime(fuzz =
yes) to add the exact amount of random bits to the time. This should happen no
matter which time function is used clock_gettime(), getclock() or gettimeofday().
Sound good?
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| Damion de Soto --------------------------------------------------
| Software Engineer email: [EMAIL PROTECTED]
| Secure Computing Corporation web: http://www.securecomputing.com
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