[Toybox] Debugging of the mkpasswd.c ASAN error (It's glibc's fault)

[Oliver Webb]

I took a closer look at the mkpassword.c error I reported in October.
The problem seems to only happen when ASAN is enabled, and is _inside_ glibc's crypt().

Putting "dprintf(2, "%p, %p, %p -- %s, %s\n", toys.optargs, toybuf, 
                      salt, *toys.optargs ? : toybuf, salt);"
Just before the final xprintf (should be xputs) call, when built with glibc and ASAN gives:

$ echo "Don't Panic" | ./mkpasswd
0x502000000010, 0x652862210180, 0x77bc39509020 -- Don't Panic, F.
AddressSanitizer:DEADLYSIGNAL
=================================================================
==70951==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000000000000 bp 0x7fff6ed82b00 sp 0x7fff6ed82a28 T0)
==70951==Hint: pc points to the zero page.
==70951==The signal is caused by a READ memory access.
==70951==Hint: address points to the zero page.
    #0 0x0  (<unknown module>)
    #1 0x6528621f38c3 in main [Path to main.c]:319
    #2 0x77bc3b957ccf  (/usr/lib/libc.so.6+0x25ccf) (BuildId: c0caa0b7709d3369ee575fcd7d7d0b0fc48733af)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (<unknown module>)
==70951==ABORTING

I would build with ASAN using musl to see if it's ASAN's problem or glibc's but I can't
get musl builds to include libasan

This isn't password.c plumbing that's wrong here, it's either glibc's or ASAN's problem.
And to fix it mkpasswd.c and any command that calls crypt() should probally be built without
ASAN if possible (Could we put something in portability.sh here to fix it? Or do we have to directly
change make.sh and/or single.sh)

-   Oliver Webb <aquahobbyist at proton.me>