This module is currently implemented to use the same technique as
libottery (later used by the bsds' arc4random replacement), using
AES-CTR-256 as its underlying stream cipher. It's backtracking-
resistant immediately after each call, and prediction-resistant
after a while.
Here's how it works:
We generate psuedorandom bytes using AES-CTR-256. We generate BUFLEN bytes
at a time. When we do this, we keep the first SEED_LEN bytes as the key
and the IV for our next invocation of AES_CTR, and yield the remaining
BUFLEN - SEED_LEN bytes to the user as they invoke the PRNG. As we yield
bytes to the user, we clear them from the buffer.
Every RESEED_AFTER times we refill the buffer, we mix in an additional
SEED_LEN bytes from our strong PRNG into the seed.
If the user ever asks for a huge number of bytes at once, we pull SEED_LEN
bytes from the PRNG and use them with our stream cipher to fill the user's
request.
Using an anonymous mmap() is a good way to get pages that we can set
kernel-level flags on, like minherit() or madvise() or mlock().
We're going to use that so that we can make uninheritable locked
pages to store PRNG data.
Because the test is adding entries to the "rend_cache" directly, the
rend_cache_increment_allocation() was never called which made the
rend_cache_clean() call trigger that underflow warning:
rend_cache/clean: [forking] Nov 29 09:55:04.024 [warn] rend_cache_decrement_allocation(): Bug: Underflow in rend_cache_decrement_allocation (on Tor 0.4.0.0-alpha-dev 2240fe63feb9a8cf)
The test is still good and valid.
Fixes#28660
Signed-off-by: David Goulet <dgoulet@torproject.org>
NOTE: This commit breaks the build, because there was a mistake in an
earlier change of exactly the sort that this is meant to detect! I'm
leaving it broken for illustration.
Test exactly what the geometric sampler returns, because that's what
the downstream callers of it are going to use.
While here, also assert that the geometric sampler returns a positive
integer. (Our geometric distribution is the one suported on {1, 2,
3, ...} that returns the number of trials before the first success,
not the one supported on {0, 1, 2, ...} that returns the number of
failures before the first success.)
Prior to this commit, the testsuite was failing on OpenBSD. After
this commit the testsuite runs fine on OpenBSD.
It was previously decided to test for the OpenBSD macro (rather than
__OpenBSD__, etc.) because OpenBSD forks seem to have the former
macro defined. sys/param.h must be included for the OpenBSD macro
definition; however, many files tested for the OpenBSD macro without
having this header included.
This commit includes sys/param.h in the files where the OpenBSD macro
is used (and sys/param.h is not already included), and it also
changes some instances of the __OpenBSD__ macro to OpenBSD.
See commit 27df23abb6 which changed
everything to use OpenBSD instead of __OpenBSD__ or OPENBSD. See
also tickets #6982 and #20980 (the latter ticket is where it was
decided to use the OpenBSD macro).
Signed-off-by: Kris Katterjohn <katterjohn@gmail.com>
