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  1. PHP Driver: Extension
  2. PHPC-733

Possible mongoc_client_t use-after-free with shutdown functions

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Critical - P2
    • Resolution: Fixed
    • Affects Version/s: 1.1.8
    • Fix Version/s: 1.2.0
    • Component/s: None
    • Labels:
      None
    • Environment:
      PHP 5.5.37 (possible other PHP 5.x, but not PHP 7)

      Description

      Jonathan H. Wage encountered a crash due to a libmongoc assert failure, where a cursor was being killed during a shutdown function:

      #0  0x0000003b20e32625 in raise (sig=<value optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
              resultvar = 0
              pid = <value optimized out>
              selftid = <value optimized out>
      #1  0x0000003b20e33e05 in abort () at abort.c:92
              save_stage = 2
              act = {__sigaction_handler = {sa_handler = 0x60, sa_sigaction = 0x60}, sa_mask = {__val = {253958350976, 47549832, 47537728, 0, 140735799216256, 1, 253955669547, 206158430256, 140735799214840,
                    140735799214624, 157312, 70326552, 228518431, 32, 140250760109120, 1454}}, sa_flags = -1396939744, sa_restorer = 0x10}
              sigs = {__val = {32, 0 <repeats 15 times>}}
      #2  0x00007f8eacb9e415 in mongoc_cluster_fetch_stream_pooled (cluster=0x2d58d88, sd=0x3e2c1d0, reconnect_ok=false, error=0x0) at src/mongoc/mongoc-cluster.c:1544
              stream = 0x7fff9b51c880
              topology = <value optimized out>
              cluster_node = <value optimized out>
              timestamp = <value optimized out>
      #3  _mongoc_cluster_stream_for_server_description (cluster=0x2d58d88, sd=0x3e2c1d0, reconnect_ok=false, error=0x0) at src/mongoc/mongoc-cluster.c:1365
              topology = <value optimized out>
              server_stream = <value optimized out>
      #4  0x00007f8eacb9e838 in mongoc_cluster_stream_for_server (cluster=0x2d58d88, server_id=3, reconnect_ok=false, error=0x0) at src/mongoc/mongoc-cluster.c:1422
              topology = <value optimized out>
              sd = 0x3e2c1d0
              server_stream = 0x0
              __func__ = "mongoc_cluster_stream_for_server"
      #5  0x00007f8eacb991a6 in _mongoc_client_kill_cursor (client=0x2d58d70, server_id=<value optimized out>, cursor_id=4536838857318534913, db=0x7fff9b51c880 "opensky_devo", collection=0x3e4b9a5 "sellables")
          at src/mongoc/mongoc-client.c:1282
              server_stream = <value optimized out>
              __func__ = "_mongoc_client_kill_cursor"
      #6  0x00007f8eacba5028 in _mongoc_cursor_destroy (cursor=0x3e4b7f0) at src/mongoc/mongoc-cursor.c:273
              db = "opensky_devo\000\000\000\000 -\321\003\000\000\000\000p\022\315\003\000\000\000\000X\000\000\000\000\000\000\000bM[\000\000\000\000\000\270\v\000\000\000\000\000\000bM[\000\000\000\000\000\220\017\000\000\000\000\000\000bM[\000\000\000\000\000 [\345\003\000\000\000\000\020Y\344\003\000\000\000\000@\002\000\000\000\000\000\000bM[\000\000\000\000\000X\000\000\000\000\000\000\000bM[\000\000\000\000"
              __func__ = "_mongoc_cursor_destroy"
      #7  0x00007f8eacdf67b2 in php_phongo_cursor_free (cursor=0x3e09b60) at /usr/src/debug/php-pecl-mongodb-1.1.8/NTS/php_phongo.c:2142
      No locals.
      #8  0x00007f8eacdedbe1 in php_phongo_cursor_free_object (object=<value optimized out>) at /usr/src/debug/php-pecl-mongodb-1.1.8/NTS/src/MongoDB/Cursor.c:226
              intern = 0x3e09b60
      #9  0x000000000060623c in zend_objects_store_free_object_storage (objects=0x9f66c0) at /usr/src/debug/php-5.5.37/Zend/zend_objects_API.c:97
              obj = <value optimized out>
              i = <value optimized out>
      #10 0x00000000005ceb23 in shutdown_executor () at /usr/src/debug/php-5.5.37/Zend/zend_execute_API.c:290
      ---Type <return> to continue, or q <return> to quit---
              __orig_bailout = 0x7fff9b51ce80
              __bailout = {{__jmpbuf = {10445600, -9101158388112889313, 140251056034432, 140251056037176, 140251056037720, 0, 9100937786234956319, -9101158395108857313}, __mask_was_saved = 0, __saved_mask = {
                    __val = {9345585548714895903, 0, 5983586, 32, 5983586, 184, 5983586, 140251056282616, 62546720, 96, 10445336, 1, 140251056034432, 140251056037176, 6139470, 10445248}}}}
      #11 0x00000000005dcce2 in zend_deactivate () at /usr/src/debug/php-5.5.37/Zend/zend.c:946
      No locals.
      #12 0x000000000057c761 in php_request_shutdown (dummy=<value optimized out>) at /usr/src/debug/php-5.5.37/main/main.c:1813
              report_memleaks = 1 '\001'
      #13 0x00000000006976c9 in main (argc=<value optimized out>, argv=<value optimized out>) at /usr/src/debug/php-5.5.37/sapi/fpm/fpm/fpm_main.c:1981
              primary_script = <value optimized out>
              __orig_bailout = 0x0
              __bailout = {{__jmpbuf = {0, 9100937787569793567, 2, 0, 10423264, 0, 9100937786052504095, -9101158278872241633}, __mask_was_saved = 0, __saved_mask = {__val = {0 <repeats 14 times>, 253950458591,
                      0}}}}
              exit_status = 0
              c = <value optimized out>
              use_extended_info = 0
              file_handle = {type = ZEND_HANDLE_FILENAME, filename = 0x7f8ebe5fd0b8 "x\324\177\002", opened_path = 0x0, handle = {fd = 0, fp = 0x0, stream = {handle = 0x0, isatty = 0, mmap = {len = 0,
                      pos = 253979787264, map = 0x3b2261d000, buf = 0x3b2261c6bc <Address 0x3b2261c6bc out of bounds>, old_handle = 0x3b2261c6bc, old_closer = 0}, reader = 0x5, fsizer = 0x3b2281c000,
                    closer = 0x3b2281e000}}, free_filename = 0 '\000'}
              orig_optind = 1
              orig_optarg = 0x0
              ini_entries_len = <value optimized out>
              max_requests = 2500
              requests = 11
              fcgi_fd = 10444256
              request = {listen_socket = 0, fd = -1, id = 1, keep = 0, closed = 0, in_len = 0, in_pad = 7, out_hdr = 0x0, out_pos = 0x7fff9b51d010 "\001\006",
                out_buf = "\001\006\000\001\000\a\001\000/html>\n\000\001\003\000\001\000\b\000\000\000\000\000\000\000he\r\nDate: Fri, 08 Jul 2016 15:24:14 GMT\r\nContent-Type: text/html; charset=UTF-8\r\nX-OSKY-P-NODE: dc1osphp01\r\n\r\n\000\000\000\000\000\001\006\000\001\330p\000\000ssion-language/Symfony/Component/ExpressionLangua"..., reserved = '\000' <repeats 15 times>, env = 0x7f8ebe5fd040}
              fpm_config = 0x0
              fpm_prefix = 0x0
              fpm_pid = 0x0
              test_conf = 0
              force_daemon = 1
              php_information = 0
              php_allow_to_run_as_root = 0
              __func__ = "main"
      

      My initial analysis:

      Also of note: before I noticed mongoc_cluster_fetch_stream_pooled() in the crash backtrace, we originally suspected this was a recurrence of PHPC-671 (fixed in 1.1.7), which entailed a crash due to PHP 5.x freeing the MongoDB\Driver\Manager object before open MongoDB\Driver\Cursor objects. That resulted in the Manager also destroying libmongoc's client object (and all streams) and causing a use-after-free when the Cursor wanted to free itself and send a kill command over the stream it was last associated with.

      That said, mongoc_cluster_fetch_stream_pooled() is really the red flag here, as there's no reason that libmongoc should not be in single_threaded mode. See the _mongoc_cluster_stream_for_server_description for the relevant logic in libmongoc (one level deep in the backtrace).

      Most likely, the MongoDB\Driver\Manager (and its mongoc_client_t) was again freed before the non-exhausted MongoDB\Driver\Cursor. This resulted in topology->single_threaded being zeroed in memory (responsible for libmongoc attempting to fetch a stream from a pool). Somehow, the mongoc_cursor_t still had a reference to this memory when it attempted to kill itself.

      Since Jonathan H. Wage was using mongo-php-adapter, this issue may be a duplicate of PHPC-732 and caused entirely by the use of generators. We'll need to confirm that.

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              Assignee:
              jmikola Jeremy Mikola
              Reporter:
              jmikola Jeremy Mikola
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                Dates

                Created:
                Updated:
                Resolved: