Stack buffer overflow ext/bcmath/libbcmath/src/div.c:464:12 in bc_divide

[YuanchengJiang]

Description

The following code:

<?php
$file = $dirname . 'tmp.zip';
$zip = new ZipArchive;
if (!$zip->open($file, ZipArchive::CREATE)) {
}
$zip->addFromString('�', __FILE__, ZipArchive::FL_ENC_UTF_8);
$fusion = $zip;
require(__DIR__ . "/run_bcmath_tests_function.inc");
$exponents = ["252", "-112"];
run_bcmath_tests($fusion, $exponents, "**", bcpow(...));

Resulted in this output:

=================================================================
==845608==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffedda3eff0 at pc 0x000000e6e458 bp 0x7ffedda3e380 sp 0x7ffedda3e378
WRITE of size 1 at 0x7ffedda3eff0 thread T0
    #0 0xe6e457 in bc_divide /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/bcmath/libbcmath/src/div.c:464:12
    #1 0xe83120 in bc_raise /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/bcmath/libbcmath/src/raise.c:95:7
    #2 0xe41e90 in zif_bcpow /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/bcmath/bcmath.c:618:7
    #3 0x3d67ff8 in zend_closure_internal_handler /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_closures.c:724:2
    #4 0x4291997 in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_vm_execute.h:2037:4
    #5 0x3fb01c7 in execute_ex /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_vm_execute.h:58595:7
    #6 0x3fb244c in zend_execute /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_vm_execute.h:64247:2
    #7 0x4d48a09 in zend_execute_script /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend.c:1934:3
    #8 0x355e25a in php_execute_script_ex /home/phpfuzz/WorkSpace/flowfusion/php-src/main/main.c:2577:13
    #9 0x355f398 in php_execute_script /home/phpfuzz/WorkSpace/flowfusion/php-src/main/main.c:2617:9
    #10 0x4d5cd1a in do_cli /home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php_cli.c:938:5
    #11 0x4d571ff in main /home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php_cli.c:1313:18
    #12 0x7f282fcddd8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #13 0x7f282fcdde3f in __libc_start_main csu/../csu/libc-start.c:392:3
    #14 0x605a64 in _start (/home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php+0x605a64)

Address 0x7ffedda3eff0 is located in stack of thread T0 at offset 496 in frame
    #0 0xe3ffff in zif_bcpow /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/bcmath/bcmath.c:571

  This frame has 8 object(s):
    [32, 40) 'base_str' (line 572)
    [64, 72) 'exponent_str' (line 572)
    [96, 104) 'scale_param' (line 573)
    [128, 129) 'scale_param_is_null' (line 574)
    [144, 152) 'first' (line 575)
    [176, 184) 'bc_exponent' (line 575)
    [208, 216) 'result' (line 575)
    [240, 496) 'bc_arena' (line 593) <== Memory access at offset 496 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/phpfuzz/WorkSpace/flowfusion/php-src/ext/bcmath/libbcmath/src/div.c:464:12 in bc_divide
Shadow bytes around the buggy address:
  0x10005bb3fda0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10005bb3fdb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10005bb3fdc0: f1 f1 f1 f1 00 f2 f2 f2 00 f2 f2 f2 00 f2 f2 f2
  0x10005bb3fdd0: 01 f2 00 f2 f2 f2 00 f2 f2 f2 00 f2 f2 f2 00 00
  0x10005bb3fde0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x10005bb3fdf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00[f3]f3
  0x10005bb3fe00: f3 f3 f3 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00
  0x10005bb3fe10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10005bb3fe20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10005bb3fe30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10005bb3fe40: 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
==845608==ABORTING

PHP Version

nightly

Operating System

ubuntu 22.04

[YuanchengJiang]

need run_bcmath_tests_function.inc in ext/bcmath/tests/

[cmb69]

Simplified reproducer:

bcpow("10", "-112", 10);