Null pointer dereference in mrb_get_args

[clayton-shopify]

The following input demonstrates a crash:

[][0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]=%
a

ASAN report:

==10182==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000018 (pc 0x00010aa9d9bb bp 0x7fff551882f0 sp 0x7fff551865a0 T0)
==10182==The signal is caused by a READ memory access.
==10182==Hint: address points to the zero page.
    #0 0x10aa9d9ba in mrb_get_args class.c:555
    #1 0x10aa828fc in mrb_ary_aset array.c:811
    #2 0x10abdcf90 in mrb_vm_exec vm.c:1259
    #3 0x10abd2619 in mrb_vm_run vm.c:823
    #4 0x10ac048f9 in mrb_top_run vm.c:2614
    #5 0x10acd57a5 in mrb_load_exec parse.y:5760
    #6 0x10acd65b5 in mrb_load_file_cxt parse.y:5769
    #7 0x10aa70066 in main mruby.c:227
    #8 0x7fffbbbba234 in start (libdyld.dylib:x86_64+0x5234)

==10182==Register values:
rax = 0x0000000000000018  rbx = 0x00007fff55186800  rcx = 0x0000000000000018  rdx = 0x0000100000000003
rdi = 0x00001c2800001400  rsi = 0x0000100000000000  rbp = 0x00007fff551882f0  rsp = 0x00007fff551865a0
 r8 = 0x0000100000000000   r9 = 0x00007fff551865c0  r10 = 0x00007fff551865d0  r11 = 0x00007fff55186610
r12 = 0x00007fff55186670  r13 = 0x00007fff55186690  r14 = 0x00007fff55186630  r15 = 0x00007fff55186650
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV class.c:555 in mrb_get_args
==10182==ABORTING
Abort trap: 6

This issue was reported by https://hackerone.com/ssarong