Polling wakeup: recover from possible faults or return error #29
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Apr 27, 2023
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
apache#1 0x7fe738f4e01c in apr_pool_walk_tree memory/unix/apr_pools.c:1505
apache#2 0x7fe738f4e066 in apr_pool_walk_tree memory/unix/apr_pools.c:1511
apache#3 0x7fe738f4e066 in apr_pool_walk_tree memory/unix/apr_pools.c:1511
apache#4 0x7fe738f4e066 in apr_pool_walk_tree memory/unix/apr_pools.c:1511
apache#5 0x7fe738f5027c in apr_pool_find memory/unix/apr_pools.c:2291
apache#6 0x7fe738f14aba in apr_table_mergen tables/apr_tables.c:746
apache#7 0x5578ad926a25 in ap_set_keepalive /home/ylavic/src/apache/httpd/trunk/modules/http/http_protocol.c:309
apache#8 0x5578ad93933f in ap_http_header_filter /home/ylavic/src/apache/httpd/trunk/modules/http/http_filters.c:1376
apache#9 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
apache#10 0x5578ad9a67f3 in ap_content_length_filter /home/ylavic/src/apache/httpd/trunk/server/protocol.c:2046
apache#11 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
apache#12 0x5578ad9405ae in ap_byterange_filter /home/ylavic/src/apache/httpd/trunk/modules/http/byterange_filter.c:463
apache#13 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
apache#14 0x7fe7330e398b in ap_headers_output_filter /home/ylavic/src/apache/httpd/trunk/modules/metadata/mod_headers.c:891
apache#15 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
apache#16 0x7fe732e32dba in session_output_filter /home/ylavic/src/apache/httpd/trunk/modules/session/mod_session.c:501
apache#17 0x5578ad98f7bd in ap_pass_brigade /home/ylavic/src/apache/httpd/trunk/server/util_filter.c:783
apache#18 0x5578ad9c8ee5 in default_handler /home/ylavic/src/apache/httpd/trunk/server/core.c:5188
apache#19 0x5578ad9431bb in ap_run_handler /home/ylavic/src/apache/httpd/trunk/server/config.c:170
apache#20 0x5578ad944941 in ap_invoke_handler /home/ylavic/src/apache/httpd/trunk/server/config.c:444
apache#21 0x5578ad92cc23 in ap_process_async_request /home/ylavic/src/apache/httpd/trunk/modules/http/http_request.c:463
apache#22 0x5578ad924d7c in ap_process_http_async_connection /home/ylavic/src/apache/httpd/trunk/modules/http/http_core.c:158
apache#23 0x5578ad925410 in ap_process_http_connection /home/ylavic/src/apache/httpd/trunk/modules/http/http_core.c:252
apache#24 0x5578ad97e04d in ap_run_process_connection /home/ylavic/src/apache/httpd/trunk/server/connection.c:42
apache#25 0x7fe735c7ef79 in process_socket /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:1097
apache#26 0x7fe735c856a0 in worker_thread /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:2386
apache#27 0x7fe738f7cef4 in dummy_worker threadproc/unix/thread.c:145
apache#28 0x7fe738e3eea6 in start_thread nptl/pthread_create.c:477
apache#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)
apache#1 0x7fe738f4e9e5 in pool_clear_debug memory/unix/apr_pools.c:1893
apache#2 0x7fe738f4ecb2 in pool_destroy_debug memory/unix/apr_pools.c:1956
apache#3 0x7fe738f4eeeb in apr_pool_destroy_debug memory/unix/apr_pools.c:2002
apache#4 0x5578ada2534b in ap_queue_info_push_pool /home/ylavic/src/apache/httpd/trunk/server/mpm_fdqueue.c:230
apache#5 0x7fe735c81412 in process_lingering_close /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:1686
apache#6 0x7fe735c7f9bc in process_socket /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:1255
apache#7 0x7fe735c856a0 in worker_thread /home/ylavic/src/apache/httpd/trunk/server/mpm/event/event.c:2386
apache#8 0x7fe738f7cef4 in dummy_worker threadproc/unix/thread.c:145
apache#9 0x7fe738e3eea6 in start_thread nptl/pthread_create.c:477
git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.7.x@1883751 13f79535-47bb-0310-9956-ffa450edef68
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Good time of day.
We've noticed that there is a bug when wakeup pipe in polling becomes broken that leads to an instant taint of polling process
It is possible because in Windows pipe is done via real network sockets that could be closed by network change or in some other cases
In general, no matter the OS if wakeup pipe gets broken
apr_poll_drain_wakeup_pipe's status is disregarded and no action is takenThis PR is mirroring mailing list message