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Bug #81691 use-after-free of spl file handle
Submitted: 2021-12-03 08:44 UTC Modified: 2021-12-04 06:47 UTC
Avg. Score:1.0 ± 0.0
Reproduced:0 of 1 (0.0%)
From: cuirongzhen at huawei dot com Assigned:
Status: Open Package: SPL related
PHP Version: 8.1.0 OS: openEuler/Ubuntu 20.04.1
Private report: No CVE-ID: None
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From: cuirongzhen at huawei dot com
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 [2021-12-03 08:44 UTC] cuirongzhen at huawei dot com
Usually $file=SplFileObject(..) can be closed with $file=null.
However, fclose(end(get_resources())); can directly free the file stream without set $file to null.
It can cause use-after-free if $file gets accessed later.

Test script:
  $file=new SplFileObject("/tmp/1.txt");

Expected result:
report error at $file->fgets()

Actual result:
Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00005555559b83c9 in _php_stream_fill_read_buffer (stream=stream@entry=0x7ffff567e2a0, size=<optimized out>) at ./php-8.1.0-src/main/streams/streams.c:666
#2  0x00005555559b895f in _php_stream_get_line (stream=0x7ffff567e2a0, buf=buf@entry=0x0, maxlen=maxlen@entry=0, returned_len=returned_len@entry=0x7fffffffaa40)
    at ./php-8.1.0-src/main/streams/streams.c:981
#3  0x0000555555901110 in spl_filesystem_file_read (intern=0x7ffff5682000, silent=0) at ./php-8.1.0-src/ext/spl/spl_directory.c:1887
#4  0x00005555559014ff in zim_SplFileObject_fgets (execute_data=<optimized out>, return_value=0x7ffff56140e0) at ./php-8.1.0-src/ext/spl/spl_directory.c:2174
#5  0x0000555555a73363 in ZEND_DO_FCALL_SPEC_RETVAL_USED_HANDLER () at ./php-8.1.0-src/Zend/zend_vm_execute.h:1870
#6  execute_ex (ex=0x7ffff567e2a0) at ./php-8.1.0-src/Zend/zend_vm_execute.h:54555
#7  0x0000555555a74f14 in zend_execute (op_array=0x7ffff568a000, return_value=0x0) at ./php-8.1.0-src/Zend/zend_vm_execute.h:58882
#8  0x0000555555a084ab in zend_execute_scripts (type=type@entry=8, retval=retval@entry=0x0, file_count=file_count@entry=3) at ./php-8.1.0-src/Zend/zend.c:1761
#9  0x00005555559a471a in php_execute_script (primary_file=<optimized out>) at ./php-8.1.0-src/main/main.c:2534
#10 0x0000555555aeaf9b in do_cli (argc=2, argv=0x555556788ed0) at ./php-8.1.0-src/sapi/cli/php_cli.c:965
#11 0x000055555578f052 in main (argc=2, argv=0x555556788ed0) at ./php-8.1.0-src/sapi/cli/php_cli.c:1367


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 [2021-12-03 10:52 UTC]
Thanks for reporting this issue!  I don't think this qualifies as
security issue, but it is certainly bad that the underlying
resource can be accessed directly without the knowledge of the
object, which causes all kinds of issues (e.g. changing the stream
position on the resource would not cause a segfault, but other
erroneous behavior).
 [2021-12-04 06:47 UTC]
-Type: Security +Type: Bug
 [2022-01-12 20:09 UTC] camporter1 at gmail dot com
The following pull request has been associated:

Patch Name: [SPL] Prevent fclose on underlying SplFileObject file stream.
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