ASan stack-buffer-overflow src/quant.c:1390 in sixel_quant_apply_palette

[fgeek]

libsixel-stack-buffer-overflow-quant.c-1390-sixel_quant_apply_palette.png.zip (SHA1: 56193b1ec3d33cc6633c9a27cf0835f88d04b748)
Tested commit: 5db717d
Credit: Henri Salo
Tools: american fuzzy lop 2.52b, afl-utils
Thanks to Kapsi internet-käyttäjät ry for providing valuable fuzzing resources.

./bin/img2sixel -o test libsixel-stack-buffer-overflow-quant.c-1390-sixel_quant_apply_palette.png
=================================================================
==14215==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffe68b3919e at pc 0x7fa061ccdb1d bp 0x7ffe68b39080 sp 0x7ffe68b39078
READ of size 2 at 0x7ffe68b3919e thread T0
    #0 0x7fa061ccdb1c in sixel_quant_apply_palette /home/hsalo/src/libsixel/src/quant.c:1390
    #1 0x7fa061cd0ca3 in sixel_dither_apply_palette /home/hsalo/src/libsixel/src/dither.c:786
    #2 0x7fa061cc0181 in sixel_encode_dither /home/hsalo/src/libsixel/src/tosixel.c:787
    #3 0x7fa061cc0181 in sixel_encode /home/hsalo/src/libsixel/src/tosixel.c:1488
    #4 0x7fa061d7c6a9 in sixel_encoder_output_without_macro /home/hsalo/src/libsixel/src/encoder.c:819
    #5 0x7fa061d7f6b8 in sixel_encoder_encode_frame /home/hsalo/src/libsixel/src/encoder.c:1049
    #6 0x7fa061d5dcea in load_with_builtin /home/hsalo/src/libsixel/src/loader.c:913
    #7 0x7fa061d6b7f8 in sixel_helper_load_image_file /home/hsalo/src/libsixel/src/loader.c:1352
    #8 0x7fa061d8c7de in sixel_encoder_encode /home/hsalo/src/libsixel/src/encoder.c:1734
    #9 0x564ccc870bab in main /home/hsalo/src/libsixel/converters/img2sixel.c:457
    #10 0x7fa060f132e0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202e0)
    #11 0x564ccc870de9 in _start (/home/hsalo/builds/libsixel/5db717dfef6fa327cd4025e7352550f63d20699c/bin/img2sixel+0x2de9)

Address 0x7ffe68b3919e is located in stack of thread T0 at offset 94 in frame
    #0 0x7fa061ccabdf in sixel_quant_apply_palette /home/hsalo/src/libsixel/src/quant.c:1257

  This frame has 3 object(s):
    [32, 36) 'copy'
    [96, 608) 'migration_map' <== Memory access at offset 94 underflows this variable
    [640, 1664) 'new_palette'
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/hsalo/src/libsixel/src/quant.c:1390 in sixel_quant_apply_palette
Shadow bytes around the buggy address:
  0x10004d15f1e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f1f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f210: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f220: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f4 f4 f4
=>0x10004d15f230: f2 f2 f2[f2]00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f240: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f250: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f260: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004d15f270: 00 00 00 00 f2 f2 f2 f2 00 00 00 00 00 00 00 00
  0x10004d15f280: 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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==14215==ABORTING

[saitoha]

@fgeek thank you!