Why not use nonblocking pool and seed nonblocking pool only with half of collected entropy to get /dev/random in almost all practical scenarios nonblocking?
On Thu, Dec 13, 2012 at 08:44:36AM +0100, Stephan Mueller wrote: > On 13.12.2012 01:43:21, +0100, Andrew Morton > <a...@linux-foundation.org> wrote: > > Hi Andrew, > > On Tue, 11 Dec 2012 13:33:04 +0100 > > Stephan Mueller <smuel...@chronox.de> wrote: > > > >> Some time ago, I noticed the fact that for every newly > >> executed process, the function create_elf_tables requests 16 bytes of > >> randomness from get_random_bytes. This is easily visible when calling > >> > >> while [ 1 ] > >> do > >> cat /proc/sys/kernel/random/entropy_avail > >> sleep 1 > >> done > > Please see > > http://ozlabs.org/~akpm/mmotm/broken-out/binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patch > > > > That patch is about one week from a mainline merge, btw. > > Initially I was also thinking about get_random_int. But stack protection > depends on non-predictable numbers to ensure it cannot be defeated. As > get_random_int depends on MD5 which is assumed to be broken now, I > discarded the idea of using get_random_int. > > Moreover, please consider that get_cycles is an architecture-specific > function that on some architectures only returns 0 (For all > architectures where this is implemented, you have no guarantee that it > increments as a high-resolution timer). So, the quality of > get_random_int is questionable IMHO for the use as a stack protector. > > Also note, that other in-kernel users of get_random_bytes may be > converted to using the proposed kernel pool to avoid more entropy drainage. > > Please note that the suggested approach of fully seeding a deterministic > RNG never followed by a re-seeding is used elsewhere (e.g. the OpenSSL > RNG). Therefore, I think the suggested approach is viable. > > Ciao > Stephan > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- It's those computer people in X {city of world}. They keep stuffing things up. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
