OOB read when starting up file cache

[YuanchengJiang]

Description

The following code:

no need php code

Resulted in this output:

==1891326==ERROR: AddressSanitizer: global-buffer-overflow on address 0x0000085d7ec0 at pc 0x000000623708 bp 0x7fff6a64c320 sp 0x7fff6a64baa0
READ of size 33 at 0x0000085d7ec0 thread T0
    #0 0x623707 in printf_common(void*, char const*, __va_list_tag*) (/home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php+0x623707)
    #1 0x7efd7cabdbe5 in zend_accel_error_va_args /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/opcache/zend_accelerator_debug.c:79:3
    #2 0x7efd7cabc7de in zend_accel_error /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/opcache/zend_accelerator_debug.c:103:2
    #3 0x7efd7cd28095 in accel_post_startup /home/phpfuzz/WorkSpace/flowfusion/php-src/ext/opcache/ZendAccelerator.c:3334:3
    #4 0x4d33854 in zend_post_startup /home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend.c:1105:7
    #5 0x354ec4f in php_module_startup /home/phpfuzz/WorkSpace/flowfusion/php-src/main/main.c:2326:6
    #6 0x4d60378 in php_cli_startup /home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php_cli.c:397:9
    #7 0x4d56199 in main /home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php_cli.c:1280:6
    #8 0x7efd8469ad8f  (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f)
    #9 0x7efd8469ae3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e3f)
    #10 0x605934 in _start (/home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php+0x605934)

0x0000085d7ec0 is located 32 bytes to the left of global variable 'main_cwd_state' defined in '/home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_virtual_cwd.c:92:18' (0x85d7ee0) of size 16
0x0000085d7ec0 is located 0 bytes to the right of global variable 'zend_system_id' defined in '/home/phpfuzz/WorkSpace/flowfusion/php-src/Zend/zend_system_id.c:24:15' (0x85d7ea0) of size 32
SUMMARY: AddressSanitizer: global-buffer-overflow (/home/phpfuzz/WorkSpace/flowfusion/php-src/sapi/cli/php+0x623707) in printf_common(void*, char const*, __va_list_tag*)
Shadow bytes around the buggy address:
  0x0000810b2f80: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x0000810b2f90: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x0000810b2fa0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x0000810b2fb0: f9 f9 f9 f9 04 f9 f9 f9 f9 f9 f9 f9 00 00 00 00
  0x0000810b2fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f9
=>0x0000810b2fd0: f9 f9 f9 f9 00 00 00 00[f9]f9 f9 f9 00 00 f9 f9
  0x0000810b2fe0: f9 f9 f9 f9 04 f9 f9 f9 f9 f9 f9 f9 00 f9 f9 f9
  0x0000810b2ff0: f9 f9 f9 f9 00 f9 f9 f9 f9 f9 f9 f9 00 00 00 00
  0x0000810b3000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0000810b3010: 00 00 00 00 00 f9 f9 f9 f9 f9 f9 f9 00 f9 f9 f9
  0x0000810b3020: f9 f9 f9 f9 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
==1891326==ABORTING

To reproduce:

./php-src/sapi/cli/php -d "zend_extension=/home/phpfuzz/WorkSpace/flowfusion/php-src/modules/opcache.so" -d "opcache.enable_cli=1" -d "opcache.file_cache="/test"" -d "opcache.log_verbosity_level=4"

PHP Version

nightly

Operating System

ubuntu 22.04

[cmb69]

It seems that the zend_system_id is not yet finalized at this point in time, so is not yet zero-terminated.

 ext/opcache/ZendAccelerator.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ext/opcache/ZendAccelerator.c b/ext/opcache/ZendAccelerator.c
index 3cc5097234..3bb69eb107 100644
--- a/ext/opcache/ZendAccelerator.c
+++ b/ext/opcache/ZendAccelerator.c
@@ -3331,7 +3331,7 @@ static zend_result accel_post_startup(void)
 	}
 
 	if ( ZCG(accel_directives).file_cache ) {
-		zend_accel_error(ACCEL_LOG_INFO, "opcache.file_cache running with PHP build ID: %s", zend_system_id);
+		zend_accel_error(ACCEL_LOG_INFO, "opcache.file_cache running with PHP build ID: %.32s", zend_system_id);
 
 		zend_stat_t buf = {0};
 

This patch would fix the overflow, but would not necessarily output the correct zend_system_id. That's unfortunate, because the system ID is used as directory name in the file cache.

[cmb69]

Nope, zend_system_id is finalized there; it's just that it's never zero-terminated, so patch above is correct.