Created attachment 411754 [details] poc Hi, I found a stack-use-after-scope in expand_mmac_params at asm/preproc.c:4931 It is triggered in nasm version 2.15. Please run following command nasm -o /dev/null -f bin $PoC Here's ASAN LOG ==30308==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7ffc324707c0 at pc 0x00000062e905 bp 0x7ffc32470790 sp 0x7ffc32470788 WRITE of size 8 at 0x7ffc324707c0 thread T0 #0 0x62e904 in expand_mmac_params /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/preproc.c:4931:11 #1 0x5e8123 in pp_tokline /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/preproc.c:6361:21 #2 0x5e8123 in pp_getline /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/preproc.c:6428 #3 0x50a7f9 in assemble_file /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/nasm.c:1630:24 #4 0x50a7f9 in main /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/nasm.c:637 #5 0x7f2ca11a5b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310 #6 0x41a4a9 in _start (/mnt/hda2/suhwan/BUG_AFL/ezxml_fuzzing/nasm+0x41a4a9) Address 0x7ffc324707c0 is located in stack of thread T0 at offset 32 in frame #0 0x61fc6f in expand_mmac_params /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/preproc.c:4749 This frame has 5 object(s): [32, 40) 'newlist.i249' (line 979) <== Memory access at offset 32 is inside this variable [64, 72) 'newlist.i' (line 1002) [96, 104) 'thead' (line 4750) [128, 136) 'ep' (line 4816) [160, 168) 'ep36' (line 4834) 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-use-after-scope /home/suhwan/project/program/nasm-2.15rc0-20191023/asm/preproc.c:4931:11 in expand_mmac_params Shadow bytes around the buggy address: 0x1000064860a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1000064860b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1000064860c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1000064860d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x1000064860e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =>0x1000064860f0: 00 00 00 00 f1 f1 f1 f1[f8]f2 f2 f2 f8 f2 f2 f2 0x100006486100: 00 f2 f2 f2 f8 f2 f2 f2 f8 f3 f3 f3 00 00 00 00 0x100006486110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100006486120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100006486130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100006486140: f1 f1 f1 f1 f8 f2 f2 f2 f8 f2 f2 f2 f8 f2 f2 f2 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 ==30308==ABORTING NASM version 2.15rc0-20191023 compiled on Dec 9 2019
Doesn't trigger in nasm-2.15.04rc5-4-g51e23ac7