tree 5d53eff0fe66656380c7cf18fd98a6d8dd5d8df6
parent 37e773fd76e806ce9ecf72ed983f92a76ab0550c
author Yann Ylavic <ylavic@apache.org> 1606143965 +0000
committer Yann Ylavic <ylavic@apache.org> 1606143965 +0000

apr_pools: lock parent pool in pool_destroy_debug().

By using apr_pool_clear_debug() instead of pool_clear_debug() in
pool_destroy_debug() we gain the locking provided by the former and thus
protection from concurrent access from apr_pool_walk_tree(), which is
undefined behaviour.

While pool_destroy_debug()=>apr_pool_clear_debug()=>pool_clear_debug() calls
pool_destroy_debug() for all the children pools, this does not cause a deadlock
because apr_pool_clear_debug() locks the parent pool only (not the pool itself)
and thus pool_destroy_debug(pool->child) locks the current pool with no issue.

This fixes use-after-free like the below in httpd (with -D APR_POOL_DEBUG):

=================================================================
==2026856==ERROR: AddressSanitizer: heap-use-after-free on address 0x60600025acf0 at pc 0x7fe738f4c5be bp 0x7fe718598110 sp 0x7fe718598108
READ of size 8 at 0x60600025acf0 thread T51
    #0 0x7fe738f4c5bd in apr_thread_mutex_lock locks/unix/thread_mutex.c:124
    #1 0x7fe738f4e01c in apr_pool_walk_tree memory/unix/apr_pools.c:1505
    #2 0x7fe738f4e066 in apr_pool_walk_tree memory/unix/apr_pools.c:1511
    #3 0x7fe738f4e066 in apr_pool_walk_tree memory/unix/apr_pools.c:1511
    #4 0x7fe738f4e066 in apr_pool_walk_tree memory/unix/apr_pools.c:1511
    #5 0x7fe738f5027c in apr_pool_find memory/unix/apr_pools.c:2291
    #6 0x7fe738f14aba in apr_table_mergen tables/apr_tables.c:746
    #7 0x5578ad926a25 in ap_set_keepalive /home/ylavic/src/apache/httpd/trunk/modules/http/http_protocol.c:309
    #8 0x5578ad93933f in ap_http_header_filter /home/ylavic/src/apache/httpd/trunk/modules/http/http_filters.c:1376
    #9 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
    #10 0x5578ad9a67f3 in ap_content_length_filter /home/ylavic/src/apache/httpd/trunk/server/protocol.c:2046
    #11 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
    #12 0x5578ad9405ae in ap_byterange_filter /home/ylavic/src/apache/httpd/trunk/modules/http/byterange_filter.c:463
    #13 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
    #14 0x7fe7330e398b in ap_headers_output_filter /home/ylavic/src/apache/httpd/trunk/modules/metadata/mod_headers.c:891
    #15 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
    #16 0x7fe732e32dba in session_output_filter /home/ylavic/src/apache/httpd/trunk/modules/session/mod_session.c:501
    #17 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
    #18 0x5578ad9c8ee5 in default_handler /home/ylavic/src/apache/httpd/trunk/server/core.c:5188
    #19 0x5578ad9431bb in ap_run_handler /home/ylavic/src/apache/httpd/trunk/server/config.c:170
    #20 0x5578ad944941 in ap_invoke_handler /home/ylavic/src/apache/httpd/trunk/server/config.c:444
    #21 0x5578ad92cc23 in ap_process_async_request /home/ylavic/src/apache/httpd/trunk/modules/http/http_request.c:463
    #22 0x5578ad924d7c in ap_process_http_async_connection /home/ylavic/src/apache/httpd/trunk/modules/http/http_core.c:158
    #23 0x5578ad925410 in ap_process_http_connection /home/ylavic/src/apache/httpd/trunk/modules/http/http_core.c:252
    #24 0x5578ad97e04d in ap_run_process_connection /home/ylavic/src/apache/httpd/trunk/server/connection.c:42
    #25 0x7fe735c7ef79 in process_socket /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:1097
    #26 0x7fe735c856a0 in worker_thread /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:2386
    #27 0x7fe738f7cef4 in dummy_worker threadproc/unix/thread.c:145
    #28 0x7fe738e3eea6 in start_thread nptl/pthread_create.c:477
    #29 0x7fe738d6ed4e in __clone (/lib/x86_64-linux-gnu/libc.so.6+0xfdd4e)

0x60600025acf0 is located 48 bytes inside of 64-byte region [0x60600025acc0,0x60600025ad00)
freed by thread T63 here:
    #0 0x7fe7391ed277 in __interceptor_free (/usr/lib/x86_64-linux-gnu/libasan.so.5+0x107277)
    #1 0x7fe738f4e9e5 in pool_clear_debug memory/unix/apr_pools.c:1893
    #2 0x7fe738f4ecb2 in pool_destroy_debug memory/unix/apr_pools.c:1956
    #3 0x7fe738f4eeeb in apr_pool_destroy_debug memory/unix/apr_pools.c:2002
    #4 0x5578ada2534b in ap_queue_info_push_pool /home/ylavic/src/apache/httpd/trunk/server/mpm_fdqueue.c:230
    #5 0x7fe735c81412 in process_lingering_close /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:1686
    #6 0x7fe735c7f9bc in process_socket /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:1255
    #7 0x7fe735c856a0 in worker_thread /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:2386
    #8 0x7fe738f7cef4 in dummy_worker threadproc/unix/thread.c:145
    #9 0x7fe738e3eea6 in start_thread nptl/pthread_create.c:477


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1883750 13f79535-47bb-0310-9956-ffa450edef68