Created attachment 411656 [details] file which causes overflow Hi, when fuzzing the disassembler with honggfuzz, I discovered a stack buffer overflow in disasm.c, on line 571. Following is a detailed backtrace as supplied by the address sanitizer: ================================================================= ==640==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffcc6090bc0 at pc 0x5596a2d6cffd bp 0x7ffcc60902f0 sp 0x7ffcc60902e8 READ of size 2 at 0x7ffcc6090bc0 thread T0 #0 0x5596a2d6cffc in matches disasm/disasm.c:571 #1 0x5596a2d6cffc in disasm disasm/disasm.c:1303 #2 0x5596a2d52e54 in main disasm/ndisasm.c:319 #3 0x7f67f86bca86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21a86) #4 0x5596a2d55209 in _start (/home/jfe/nasm/ndisasm+0xb9209) Address 0x7ffcc6090bc0 is located in stack of thread T0 at offset 352 in frame #0 0x5596a2d5156f in main disasm/ndisasm.c:81 This frame has 6 object(s): [32, 33) 'rn_error' [96, 100) 'synclen' [160, 168) 'ep' [224, 240) 'prefer' [288, 352) 'buffer' <== Memory access at offset 352 overflows this variable [384, 640) 'outbuf' 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 disasm/disasm.c:571 in matches Shadow bytes around the buggy address: 0x100018c0a120: 00 00 00 00 00 00 f2 f2 f3 f3 f3 f3 00 00 00 00 0x100018c0a130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100018c0a140: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 0x100018c0a150: 01 f2 f2 f2 f2 f2 f2 f2 04 f2 f2 f2 f2 f2 f2 f2 0x100018c0a160: 00 f2 f2 f2 f2 f2 f2 f2 00 00 f2 f2 f2 f2 f2 f2 =>0x100018c0a170: 00 00 00 00 00 00 00 00[f2]f2 f2 f2 00 00 00 00 0x100018c0a180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100018c0a190: 00 00 00 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 0x100018c0a1a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100018c0a1b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100018c0a1c0: 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 ==640==ABORTING This bug can be reproduced by running "ndisasm /dev/stdin < min" where min is the attached file. However it is only visible when ndisasm is compiled with the address sanitizer.