Heap buffer overflow in ary_fill_with_nil (regression)

[clayton-shopify]

The commit aa8121c reintroduced #3353. The same input now causes a crash again:

(Array.new)[0x7fffffff] = 1

ASAN report:

==58934==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60600000a1a0 at pc 0x000103e0e4ca bp 0x7fff5c1fd630 sp 0x7fff5c1fcde0
WRITE of size 16 at 0x60600000a1a0 thread T0
    #0 0x103e0e4c9 in __asan_memcpy (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x4d4c9)
    #1 0x1039ff145 in ary_fill_with_nil array.c:104
    #2 0x103a03409 in mrb_ary_set array.c:576
    #3 0x103a0de93 in mrb_ary_aset array.c:825
    #4 0x103b670ad in mrb_vm_exec (mruby:x86_64+0x10016f0ad)
    #5 0x103b5ba74 in mrb_vm_run (mruby:x86_64+0x100163a74)
    #6 0x103b910ff in mrb_top_run (mruby:x86_64+0x1001990ff)
    #7 0x103c6926d in mrb_load_exec (mruby:x86_64+0x10027126d)
    #8 0x103c6a085 in mrb_load_file_cxt (mruby:x86_64+0x100272085)
    #9 0x1039fa933 in main mruby.c:227
    #10 0x7fffe5638234 in start (libdyld.dylib:x86_64+0x5234)

0x60600000a1a0 is located 0 bytes to the right of 64-byte region [0x60600000a160,0x60600000a1a0)
allocated by thread T0 here:
    #0 0x103e17520 in wrap_realloc (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x56520)
    #1 0x103aef385 in mrb_default_allocf (mruby:x86_64+0x1000f7385)
    #2 0x103a70348 in mrb_realloc_simple gc.c:204
    #3 0x103a70a9e in mrb_realloc gc.c:218
    #4 0x1039feebb in ary_expand_capa array.c:193
    #5 0x103a032c0 in mrb_ary_set array.c:575
    #6 0x103a0de93 in mrb_ary_aset array.c:825
    #7 0x103b670ad in mrb_vm_exec (mruby:x86_64+0x10016f0ad)
    #8 0x103b5ba74 in mrb_vm_run (mruby:x86_64+0x100163a74)
    #9 0x103b910ff in mrb_top_run (mruby:x86_64+0x1001990ff)
    #10 0x103c6926d in mrb_load_exec (mruby:x86_64+0x10027126d)
    #11 0x103c6a085 in mrb_load_file_cxt (mruby:x86_64+0x100272085)
    #12 0x1039fa933 in main mruby.c:227
    #13 0x7fffe5638234 in start (libdyld.dylib:x86_64+0x5234)

SUMMARY: AddressSanitizer: heap-buffer-overflow (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x4d4c9) in __asan_memcpy
Shadow bytes around the buggy address:
  0x1c0c000013e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c0c000013f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c0c00001400: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c0c00001410: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x1c0c00001420: fa fa fa fa fa fa fa fa fa fa fa fa 00 00 00 00
=>0x1c0c00001430: 00 00 00 00[fa]fa fa fa fd fd fd fd fd fd fd fd
  0x1c0c00001440: fa fa fa fa 00 00 00 00 00 00 00 00 fa fa fa fa
  0x1c0c00001450: fd fd fd fd fd fd fd fd fa fa fa fa 00 00 00 00
  0x1c0c00001460: 00 00 00 00 fa fa fa fa 00 00 00 00 00 00 00 00
  0x1c0c00001470: fa fa fa fa 00 00 00 00 00 00 00 00 fa fa fa fa
  0x1c0c00001480: 00 00 00 00 00 00 00 04 fa fa fa fa 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==58934==ABORTING
Abort trap: 6

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

[matz]

Sorry for regression. Fixed by bf1cb87