Date: Wed, 5 Sep 2018 08:57:37 +0100 From: Mark R V Murray <markm@FreeBSD.org> To: cem@freebsd.org Cc: Lev Serebryakov <lev@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>, freebsd-fs <freebsd-fs@freebsd.org>, Xin LI <delphij@freebsd.org> Subject: Re: newfs silently fails if random is not ready (?) Message-ID: <4637985A-28EF-4A6B-B8A6-764A86005E6B@FreeBSD.org> In-Reply-To: <CAG6CVpV7h5cuhC1o1qEqj%2BCxdnU1AHE4mPJW9KM4UCGv_u-%2BYA@mail.gmail.com> References: <609400979.20180904230820@serebryakov.spb.ru> <CAG6CVpWzaBGvEdpNBrMQSPkxBn6pybP0SWyuYUhg0Qev4RvLwA@mail.gmail.com> <1942661439.20180904235514@serebryakov.spb.ru> <CAG6CVpWmXPUZAozTdJa%2BrczVyo9wHqr=uLP2U-O%2BPytSWr6_Ug@mail.gmail.com> <774228883.20180905001035@serebryakov.spb.ru> <CAG6CVpV7h5cuhC1o1qEqj%2BCxdnU1AHE4mPJW9KM4UCGv_u-%2BYA@mail.gmail.com>
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[-- Attachment #1 --]
Nice catch! Thanks :-)
M
> On 5 Sep 2018, at 04:13, Conrad Meyer <cem@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
> @@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
>
> #ifdef _KERNEL
> #include <sys/param.h>
> +#include <sys/fail.h>
> #include <sys/kernel.h>
> #include <sys/lock.h>
> #include <sys/malloc.h>
> @@ -384,6 +385,17 @@ 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
> @@ -442,5 +454,11 @@ 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
> _______________________________________________
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> https://lists.freebsd.org/mailman/listinfo/freebsd-current
> To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"
>
--
Mark R V Murray
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