Differential up here: https://reviews.freebsd.org/D17049 for any lurkers I didn't manage to tag in the review. Best, Conrad On Wed, Sep 5, 2018 at 12:57 AM, Mark R V Murray <markm_at_freebsd.org> wrote: > Nice catch! Thanks :-) > > M > > >> On 5 Sep 2018, at 04:13, Conrad Meyer <cem_at_FreeBSD.org> wrote: >> >> Hi Lev, >> >> I took a first attempt at reproducing this problem on a fast >> desktop-class system. First steps, give us a way to revert back to >> unseeded status: >> >> --- a/sys/dev/random/fortuna.c >> +++ b/sys/dev/random/fortuna.c >> _at__at_ -39,6 +39,7 _at__at_ __FBSDID("$FreeBSD$"); >> >> #ifdef _KERNEL >> #include <sys/param.h> >> +#include <sys/fail.h> >> #include <sys/kernel.h> >> #include <sys/lock.h> >> #include <sys/malloc.h> >> _at__at_ -384,6 +385,17 _at__at_ random_fortuna_pre_read(void) >> return; >> } >> >> + /* >> + * When set, pretend we do not have enough entropy to reseed yet. >> + */ >> + KFAIL_POINT_CODE(DEBUG_FP, random_fortuna_pre_read, { >> + if (RETURN_VALUE != 0) { >> + RANDOM_RESEED_UNLOCK(); >> + return; >> + } >> + }); >> + >> + >> #ifdef _KERNEL >> fortuna_state.fs_lasttime = now; >> #endif >> _at__at_ -442,5 +454,11 _at__at_ bool >> random_fortuna_seeded(void) >> { >> >> + /* When set, act as if we are not seeded. */ >> + KFAIL_POINT_CODE(DEBUG_FP, random_fortuna_seeded, { >> + if (RETURN_VALUE != 0) >> + fortuna_state.fs_counter = UINT128_ZERO; >> + }); >> + >> return (!uint128_is_zero(fortuna_state.fs_counter)); >> } >> >> >> Second step, enable the failpoints and launch repro program: >> >> $ sudo sysctl debug.fail_point.random_fortuna_pre_read='return(1)' >> debug.fail_point.random_fortuna_pre_read: off -> return(1) >> $ sudo sysctl debug.fail_point.random_fortuna_seeded='return(1)' >> debug.fail_point.random_fortuna_seeded: off -> return(1) >> >> $ cat ./blocked_random_poc.c >> #include <stdio.h> >> #include <stdlib.h> >> #include <unistd.h> >> >> int >> main(int argc, char **argv) >> { >> printf("%x\n", arc4random()); >> return (0); >> } >> >> >> $ ./blocked_random_poc >> ... >> >> >> Third step, I looked at what that process was doing: >> >> Curiously, it is not in getrandom() at all, but instead the ARND >> sysctl fallback. I probably need to rebuild world (libc) to test this >> (new libc arc4random based on Chacha). >> >> $ procstat -kk 1196 >> PID TID COMM TDNAME KSTACK >> 1196 100435 blocked_random_poc - read_random+0x3d >> sysctl_kern_arnd+0x3a sysctl_root_handler_locked+0x89 >> sysctl_root.isra.8+0x167 userland_sysctl+0x126 sys___sysctl+0x7b >> amd64_syscall+0x940 fast_syscall_common+0x101 >> >> >> When I unblocked the failpoints, it completed successfully: >> >> $ sudo sysctl debug.fail_point.random_fortuna_pre_read='off' >> debug.fail_point.random_fortuna_pre_read: return(1) -> off >> $ sudo sysctl debug.fail_point.random_fortuna_seeded=off >> debug.fail_point.random_fortuna_seeded: return(1) -> off >> >> ... >> 9e5eb30f >> >> >> Best, >> Conrad >> _______________________________________________ >> freebsd-current_at_freebsd.org mailing list >> https://lists.freebsd.org/mailman/listinfo/freebsd-current >> To unsubscribe, send any mail to "freebsd-current-unsubscribe_at_freebsd.org" >> > > -- > Mark R V Murray >Received on Wed Sep 05 2018 - 13:40:20 UTC
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