[Bug sanitizer/105107] New: false positive stack-buffer-overflow in ASAN

[Bug sanitizer/105107] New: false positive stack-buffer-overflow in ASAN

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105107

            Bug ID: 105107
           Summary: false positive stack-buffer-overflow in ASAN
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at gcc dot gnu.org
  Target Milestone: ---

Hi,

For the following code, ASAN in gcc-O0 since 9.0 reported a
"stack-buffer-overflow", which it shouldn't.

$cat a.c
#define c(d, j) d = 5;
h=1;
*a=&h;
**b = &a;
int e;
fn1() {
  int e=0;
  int **f = &a;
  *f = &e;
}
i() {
  int g[9];
  c(**b, )
}
main() {
  fn1();
  i();
}
$
$gcc -fsanitize=address -O0 a.c;./a.out
==1==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffef6656070
at pc 0x000000401390 bp 0x7ffef6656000 sp 0x7ffef6655ff8
WRITE of size 4 at 0x7ffef6656070 thread T0
    #0 0x40138f in i /app/example.c:13
    #1 0x4013e8 in main /app/example.c:17
    #2 0x7f5a7f21c0b2 in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x240b2)
    #3 0x4010ed in _start (/app/output.s+0x4010ed)

[Bug sanitizer/105107] false positive stack-buffer-overflow in ASAN

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105107

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
There's expanded version of the testcase:

$ cat pr105107.c
int h=1;
int *a=&h;
int **b = &a;

int e;

void
fn1() {
  int e=0;
  int **f = &a;
  __builtin_printf ("addr of e=%p\n", &e);
  *f = &e;
}

void
i() {
  int g[9];
  __builtin_printf ("write to %p\n", *b);
  **b = 5;
}

int
main() {
  fn1();
  i();

  return 0;
}

$ gcc-11 pr105107.c -fsanitize=address -g && ./a.out
addr of e=0x7fffffffdaf0
write to 0x7fffffffdaf0
=================================================================
==6753==ERROR: AddressSanitizer: stack-buffer-overflow on address
0x7fffffffdaf0 at pc 0x000000401416 bp 0x7fffffffda80 sp 0x7fffffffda78
WRITE of size 4 at 0x7fffffffdaf0 thread T0
    #0 0x401415 in i /home/marxin/Programming/testcases/pr105107.c:19
    #1 0x401493 in main /home/marxin/Programming/testcases/pr105107.c:25
    #2 0x7ffff73be62f in __libc_start_call_main
../sysdeps/nptl/libc_start_call_main.h:58
    #3 0x7ffff73be6ef in __libc_start_main_impl ../csu/libc-start.c:392
    #4 0x4010f4 in _start (/home/marxin/Programming/testcases/a.out+0x4010f4)

Address 0x7fffffffdaf0 is located in stack of thread T0 at offset 96 in frame
    #0 0x401305 in i /home/marxin/Programming/testcases/pr105107.c:16

  This frame has 1 object(s):
    [48, 84) 'g' (line 17) <== Memory access at offset 96 overflows this
variable
HINT: this may be a false positive if your program uses some custom stack
unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow
/home/marxin/Programming/testcases/pr105107.c:19 in i
Shadow bytes around the buggy address:
  0x10007fff7b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x10007fff7b50: 00 00 f1 f1 f1 f1 f1 f1 00 00 00 00 04 f3[f3]f3
  0x10007fff7b60: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7b90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007fff7ba0: 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
==6753==ABORTING

The error is correct as it takes the address of 'e' in function 'fn1' where it
writes once fn1 returns.

[Bug sanitizer/105107] false positive stack-buffer-overflow in ASAN

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105107

--- Comment #2 from Li Shaohua <shaohua.li at inf dot ethz.ch> ---
Thanks for your prompt reply. The warning messages only appeared for -O0 and
-O3, not for -O1 and -O2. I wonder this might also be an issue.

[Bug sanitizer/105107] false positive stack-buffer-overflow in ASAN

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105107

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
You'll see it with:

gcc-11 pr105107.c -fsanitize=address -g -O2 &&
ASAN_OPTIONS=detect_stack_use_after_return=1 ./a.out
addr of e=0x7ffff39f4020
write to 0x7ffff39f4020
=================================================================
==31825==ERROR: AddressSanitizer: stack-use-after-return on address
0x7ffff39f4020 at pc 0x000000401373 bp 0x7fffffffdaf0 sp 0x7fffffffdae8
WRITE of size 4 at 0x7ffff39f4020 thread T0
    #0 0x401372 in i /home/marxin/Programming/testcases/pr105107.c:19
    #1 0x4010d1 in main /home/marxin/Programming/testcases/pr105107.c:25
    #2 0x7ffff73be62f in __libc_start_call_main
../sysdeps/nptl/libc_start_call_main.h:58
    #3 0x7ffff73be6ef in __libc_start_main_impl ../csu/libc-start.c:392
    #4 0x401134 in _start (/home/marxin/Programming/testcases/a.out+0x401134)