heap-buffer-overflow in sixel_encode_highcolor at tosixel.c:1361

[SuhwanSong]

img2sixel 1.8.3

There is a heap-buffer-overflow in sixel_encode_highcolor at tosixel.c:1361
please run following cmd to reproduce it.

img2sixel --high-color $PoC

poc
ASAN LOG

==28051==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6220000018fd at pc 0x7f6182c3fea8 bp 0x7ffde16993d0 sp 0x7ffde16993c8
READ of size 1 at 0x6220000018fd thread T0
    #0 0x7f6182c3fea7 in sixel_encode_highcolor /home/tmp/libsixel/src/tosixel.c:1361:25
    #1 0x7f6182c3fea7 in sixel_encode /home/tmp/libsixel/src/tosixel.c:1509
    #2 0x7f6182f6e5a4 in sixel_encoder_output_without_macro /home/tmp/libsixel/src/encoder.c:820:14
    #3 0x7f6182f6e5a4 in sixel_encoder_encode_frame /home/tmp/libsixel/src/encoder.c:1050
    #4 0x7f6182d2aa21 in sixel_helper_load_image_file /home/tmp/libsixel/src/loader.c:919:14
    #5 0x7f6182f66a4f in sixel_encoder_encode /home/tmp/libsixel/src/encoder.c:1737:14
    #6 0x51787f in main /home/tmp/libsixel/converters/img2sixel.c:457:22
    #7 0x7f61812cdb96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
    #8 0x41a379 in _start (/home/tmp/img2sixel+0x41a379)

0x6220000018fd is located 3 bytes to the left of 5328-byte region [0x622000001900,0x622000002dd0)
allocated by thread T0 here:
    #0 0x4da230 in __interceptor_malloc (/home/tmp/img2sixel+0x4da230)
    #1 0x7f6182f6e0ee in sixel_encoder_output_without_macro /home/tmp/libsixel/src/encoder.c:784:26
    #2 0x7f6182f6e0ee in sixel_encoder_encode_frame /home/tmp/libsixel/src/encoder.c:1050
    #3 0x7f6182d2aa21 in sixel_helper_load_image_file /home/tmp/libsixel/src/loader.c:919:14
    #4 0x7f6182f66a4f in sixel_encoder_encode /home/tmp/libsixel/src/encoder.c:1737:14
    #5 0x51787f in main /home/tmp/libsixel/converters/img2sixel.c:457:22
    #6 0x7f61812cdb96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/tmp/libsixel/src/tosixel.c:1361:25 in sixel_encode_highcolor
Shadow bytes around the buggy address:
  0x0c447fff82c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c447fff82d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c447fff82e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c447fff82f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c447fff8300: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c447fff8310: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa[fa]
  0x0c447fff8320: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c447fff8330: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c447fff8340: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c447fff8350: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c447fff8360: 00 00 00 00 00 00 00 00 00 00 00 00 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
==28051==ABORTING

[saitoha]

Fixed on v1.8.4, Thanks!