AddressSanitizer: dynamic-stack-buffer-overflow

[tankf33der]

take example code generate random strings and compile with sanitizers.

$ gcc -fsanitize=address main.c 
# ./a.out 
=================================================================
==567==ERROR: AddressSanitizer: dynamic-stack-buffer-overflow on address 0x7ffe55e4a198 at pc 0x55b34322c058 bp 0x7ffe55e4a0e0 sp 0x7ffe55e4a0d8
WRITE of size 1 at 0x7ffe55e4a198 thread T0
    #0 0x55b34322c057 in random_string (/root/chadstr/a.out+0x4057)
    #1 0x55b34322c1f6 in main (/root/chadstr/a.out+0x41f6)
    #2 0x7f2811d11d09 in __libc_start_main ../csu/libc-start.c:308
    #3 0x55b34322a249 in _start (/root/chadstr/a.out+0x2249)

Address 0x7ffe55e4a198 is located in stack of thread T0
SUMMARY: AddressSanitizer: dynamic-stack-buffer-overflow (/root/chadstr/a.out+0x4057) in random_string
Shadow bytes around the buggy address:
  0x10004abc13e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004abc13f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004abc1400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004abc1410: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004abc1420: ca ca ca ca 00 00 00 00 00 00 00 00 00 00 00 00
=>0x10004abc1430: 00 00 00[cb]cb cb cb cb 00 00 00 00 00 00 00 00
  0x10004abc1440: 00 00 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2 00 00
  0x10004abc1450: f3 f3 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x10004abc1460: 00 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004abc1470: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10004abc1480: 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
  Shadow gap:              cc
==567==ABORTING
$

[skullchap]

thnx, that was because of this char buffer[length];. forget to add +1 for nul byte. another reason why we need chadstr even for buffer allocation

[ghost]

feature