Hello,

On 25/07/18 08:34 AM, project-repo wrote:
> I let the fuzzer run again and it came up with a second heap buffer
> overflow. This time in regexp.c, line 286. Here is a backtrace as
> supplied by the address sanitizer:
> 
> =================================================================
> ==7428==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x611000000b2f at pc 0x7fee3354c574 bp 0x7ffd9adf2120 sp 0x7ffd9adf18d0
> READ of size 238 at 0x611000000b2f thread T0
>      #0 0x7fee3354c573  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x40573)
>      #1 0x55aabd6d7025 in match_regex sed/regexp.c:286
>      #2 0x55aabd6cd5a5 in do_subst sed/execute.c:1098
>      #3 0x55aabd6cd5a5 in execute_program sed/execute.c:1507
>      #4 0x55aabd6d4d5a in process_files sed/execute.c:1677
>      #5 0x55aabd6ac5a2 in main sed/sed.c:377
>      #6 0x7fee33173a86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21a86)
>      #7 0x55aabd6ad1c9 in _start (/home/jefeus/sed/sed/sed+0xc1c9)

Once again, great work - you indirectly found a 15-year-old bug,
in addition to the above heap buffer overflow.

The two attached patches should explain it in detail.

As these changes are somewhat subtle, I encourage everyone to
double-check them...

comments welcomed,
  - assaf