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mity / md4c

C Markdown parser. Fast. SAX-like interface. Compliant to CommonMark specification.
MIT License
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Heap buffer overflow in md_is_link_reference_definition_helper() #37

Closed ChijinZ closed 6 years ago

ChijinZ commented 6 years ago

command: ./md2html testfile

testcase: https://github.com/ChijinZ/security_advisories/blob/master/md4c-387bd02/crash_md_is_link_reference_definition_helper

AddressSanitizer provided information as below:

=================================================================
==7016==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x615000000280 at pc 0x00000054e1e4 bp 0x7ffdf438ab70 sp 0x7ffdf438ab68
READ of size 4 at 0x615000000280 thread T0
    #0 0x54e1e3 in md_is_link_reference_definition_helper /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:1931:33
    #1 0x5320d5 in md_is_link_reference_definition /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2213:11
    #2 0x5320d5 in md_consume_link_reference_definitions /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4648
    #3 0x5320d5 in md_end_current_block /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4694
    #4 0x52c7f7 in md_process_doc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5850:5
    #5 0x5202cb in md_parse /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5917:11
    #6 0x51a7a8 in md_render_html /home/ubuntu/fuzz/test/md4c/md2html/render_html.c:488:12
    #7 0x5195cc in process_file /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:139:11
    #8 0x5195cc in main /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:343
    #9 0x7f20771c082f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291
    #10 0x41a668 in _start (/home/ubuntu/fuzz/test/md4c/build/md2html/md2html+0x41a668)

0x615000000280 is located 0 bytes to the right of 512-byte region [0x615000000080,0x615000000280)
allocated by thread T0 here:
    #0 0x4ded00 in realloc /home/ubuntu/llvm/llvm-6.0.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:107
    #1 0x527b65 in md_push_block_bytes /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4560:27
    #2 0x527b65 in md_start_new_block /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4587
    #3 0x527b65 in md_process_line /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5820
    #4 0x527b65 in md_process_doc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5847
    #5 0x5202cb in md_parse /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5917:11
    #6 0x51a7a8 in md_render_html /home/ubuntu/fuzz/test/md4c/md2html/render_html.c:488:12
    #7 0x5195cc in process_file /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:139:11
    #8 0x5195cc in main /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:343
    #9 0x7f20771c082f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:1931:33 in md_is_link_reference_definition_helper
Shadow bytes around the buggy address:
0x0c2a7fff8000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c2a7fff8010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff8020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff8030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff8040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c2a7fff8050:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c2a7fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c2a7fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c2a7fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c2a7fff8090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c2a7fff80a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
==7016==ABORTING
mity commented 6 years ago

Reproduced it via valgrind on Linux. Failed to find some minimized test case without unprintable characters though.

mity commented 6 years ago

Fixed. Thanks for reporting it.