newfs silently fails if random is not ready (?)

[Mark R V Murray]

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
> @@ -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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> 

--
Mark R V Murray

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