Re: newfs silently fails if random is not ready (?)

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