On 05/29/2018 10:32 PM, Eric Blake wrote: > On 05/29/2018 03:24 AM, Michal Privoznik wrote: >> Now that we have strong PRNG generator implemented in >> virRandomBytes() let's use that instead of gnulib's random_r. >> >> Problem with the latter is in way we seed it: current UNIX time >> and libvirtd's PID are not that random as one might think. >> Imagine two hosts booting at the same time. There's a fair chance >> that those hosts spawn libvirtds at the same time and with the >> same PID. This will result in both daemons generating the same >> sequence of say MAC addresses [1]. >> >> 1: https://www.redhat.com/archives/libvirt-users/2018-May/msg00097.html >> >> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx> >> --- >> src/util/virrandom.c | 63 >> ++-------------------------------------------------- >> 1 file changed, 2 insertions(+), 61 deletions(-) >> > >> -static int >> -virRandomOnceInit(void) >> -{ >> - unsigned int seed = time(NULL) ^ getpid(); >> - >> -#if 0 >> - /* Normally we want a decent seed. But if reproducible debugging >> - * of a fixed pseudo-random sequence is ever required, uncomment >> - * this block to let an environment variable force the seed. */ >> - const char *debug = virGetEnvBlockSUID("VIR_DEBUG_RANDOM_SEED"); >> - >> - if (debug && virStrToLong_ui(debug, NULL, 0, &seed) < 0) >> - return -1; > > Are we sure we don't need the ability to quickly compile in a > deterministic replacement for debug in the future? I suppose there's > always git history, but this particular #if 0 was left in place for a > reason, where completely removing it makes it harder to realize that > such debugging is even possible. > Well, what we can now do is to cook a mock library that would implement gnutls_rnd() to return some deterministic number without any need to recompile libvirt at all. Therefore I don't think we should leave #if 0 in. And frankly, until I looked into this file I did not even know we have such option. Michal -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
