Stack buffer overflow in ext/bcmath/libbcmath/src/div.c:459

[YuanchengJiang]

Description

The following code:

<?php
$array = array (10);
$fusion = $array;
require(__DIR__ . "/run_bcmath_tests_function.inc");
$exponents = ["252", "-112"];
$baseNumbers = array_merge($fusion, [
]);
run_bcmath_tests($baseNumbers, $exponents, "**", bcpow(...));

Resulted in this output:

==1599205==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7f0179c71df0 at pc 0x5599a5410139 bp 0x7ffeb0b4acb0 sp 0x7ffeb0b4aca8
WRITE of size 1 at 0x7f0179c71df0 thread T0
    #0 0x5599a5410138 in bc_divide /php-src/ext/bcmath/libbcmath/src/div.c:459:12
    #1 0x5599a542466f in bc_raise /php-src/ext/bcmath/libbcmath/src/raise.c:95:3
    #2 0x5599a53e582f in zif_bcpow /php-src/ext/bcmath/bcmath.c:618:2
    #3 0x5599a7e56fac in zend_closure_internal_handler /php-src/Zend/zend_closures.c:724:2
    #4 0x5599a8343d67 in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER /php-src/Zend/zend_vm_execute.h:2037:4
    #5 0x5599a8086303 in execute_ex /php-src/Zend/zend_vm_execute.h:58565:7
    #6 0x5599a8088462 in zend_execute /php-src/Zend/zend_vm_execute.h:64217:2
    #7 0x5599a8d886e1 in zend_execute_script /php-src/Zend/zend.c:1928:3
    #8 0x5599a769a9d8 in php_execute_script_ex /php-src/main/main.c:2574:13
    #9 0x5599a769ba98 in php_execute_script /php-src/main/main.c:2614:9
    #10 0x5599a8d9be56 in do_cli /php-src/sapi/cli/php_cli.c:935:5
    #11 0x5599a8d96524 in main /php-src/sapi/cli/php_cli.c:1310:18
    #12 0x7f017d8e6d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #13 0x7f017d8e6e3f in __libc_start_main csu/../csu/libc-start.c:392:3
    #14 0x5599a4c03904 in _start (/php-src/sapi/cli/php+0x2403904) (BuildId: d9851980940e1525eb2e61068d0828e86059842d)

Address 0x7f0179c71df0 is located in stack of thread T0 at offset 496 in frame
    #0 0x5599a53e3a8f in zif_bcpow /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 /php-src/ext/bcmath/libbcmath/src/div.c:459:12 in bc_divide
Shadow bytes around the buggy address:
  0x0fe0af386360: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x0fe0af386370: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x0fe0af386380: f1 f1 f1 f1 00 f2 f2 f2 00 f2 f2 f2 00 f2 f2 f2
  0x0fe0af386390: 01 f2 00 f2 f2 f2 00 f2 f2 f2 00 f2 f2 f2 00 00
  0x0fe0af3863a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0fe0af3863b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00[f3]f3
  0x0fe0af3863c0: f3 f3 f3 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00
  0x0fe0af3863d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0fe0af3863e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0fe0af3863f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0fe0af386400: 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
==1599205==ABORTING

PHP Version

PHP 8.4.0-dev

Operating System

ubuntu 22.04

[cmb69]

Simplied reproducer:

bcpow("10", "-112", 1);