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HAProxy - Load balancer
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Willy Tarreau 670119955b Revert "OPTIM: queue: don't call pendconn_unlink() when the pendconn is not queued" 
This reverts commit b7ba1d9011. Actually
this test had already been removed in the past by commit fac0f645d
("BUG/MEDIUM: queue: make pendconn_cond_unlink() really thread-safe"),
but the condition to reproduce the bug mentioned there was not clear.

Now after analysis and a certain dose of code cleanup, things start to
appear more obvious. what happens is that if we check the presence of
the node in the tree without taking the lock, we can see the NULL at
the instant the node is being unlinked by another thread in
pendconn_process_next_strm() as part of __pendconn_unlink_prx() or
__pendconn_unlink_srv(). Till now there is no issue except that the
pendconn is not removed from the queue during this operation and that
the task is scheduled to be woken up by pendconn_process_next_strm()
with the stream being added to the list of the server's active
connections by __stream_add_srv_conn(). The first thread finishes
faster and gets back to stream_free() faster than the second one
sets the srv_conn on the stream, so stream_free() skips the s->srv_conn
test and doesn't try to dequeue the freshly queued entry. At the
very least a barrier would be needed there but we can't afford to
free the stream while it's being queued. So there's no other solution
than making sure that either __pendconn_unlink_prx() or
pendconn_cond_unlink() get the entry but never both, which is why the
lock is required around the test. A possible solution would be to set
p->target before unlinking the entry and using it to complete the test.
This would leave no dead period where the pendconn is not seen as
attached.

It is possible, yet extremely difficult, to reproduce this bug, which
was first noticed in bug #880. Running 100 servers with maxconn 1 and
maxqueue 1 on leastconn and a connect timeout of 30ms under 16 threads
with DEBUG_UAF, with a traffic making the backend's queue oscillate
around zero (typically using 250 connections with a local httpterm
server) may rarely manage to trigger a use-after-free.

No backport is needed.
2020-10-23 09:21:55 +02:00
.github DOC: overhauling github issue templates 2020-08-17 20:29:27 +02:00
contrib CONTRIB: tcploop: remove unused local variables in tcp_pause() 2020-10-22 05:17:08 +02:00
doc MEDIUM: fwlc: re-enable per-server queuing up to maxqueue 2020-10-22 18:30:25 +02:00
examples CLEANUP: assorted typo fixes in the code and comments 2020-06-26 11:27:28 +02:00
include Revert "OPTIM: queue: don't call pendconn_unlink() when the pendconn is not queued" 2020-10-23 09:21:55 +02:00
reg-tests REGTEST: cache: Add if-none-match test case 2020-10-22 16:10:20 +02:00
scripts CI: travis-ci: replace not defined SSL_LIB, SSL_INC for BotringSSL builds 2020-10-11 21:12:33 +02:00
src MEDIUM: fwlc: re-enable per-server queuing up to maxqueue 2020-10-22 18:30:25 +02:00
tests MEDIUM: config: remove the deprecated and dangerous global "debug" directive 2020-10-09 19:18:45 +02:00
.cirrus.yml CI: cirrus-ci: exclude slow reg-tests 2020-07-04 06:58:14 +02:00
.gitattributes MINOR: Commit .gitattributes 2020-09-05 16:21:59 +02:00
.gitignore CLEANUP: Update .gitignore 2020-09-12 13:11:24 +02:00
.travis.yml CI: travis-ci: help Coverity to detect BUG_ON() as a real stop 2020-10-09 09:55:53 +02:00
BRANCHES DOC: assorted typo fixes in the documentation 2020-03-09 14:45:58 +01:00
CHANGELOG [RELEASE] Released version 2.3-dev7 2020-10-17 10:31:50 +02:00
CONTRIBUTING DOC: Use gender neutral language 2020-07-26 22:35:43 +02:00
INSTALL BUILD: makefile: Update feature flags for NetBSD 2020-10-09 09:53:56 +02:00
LICENSE LICENSE: add licence exception for OpenSSL 2012-09-07 13:52:26 +02:00
MAINTAINERS REORG: include: split hathreads into haproxy/thread.h and haproxy/thread-t.h 2020-06-11 10:18:56 +02:00
Makefile BUILD: makefile: add entries to build common debugging tools 2020-10-22 05:17:08 +02:00
README DOC: create a BRANCHES file to explain the life cycle 2019-06-15 22:00:14 +02:00
ROADMAP DOC: update the outdated ROADMAP file 2019-06-15 21:59:54 +02:00
SUBVERS BUILD: use format tags in VERDATE and SUBVERS files 2013-12-10 11:22:49 +01:00
VERDATE [RELEASE] Released version 2.3-dev7 2020-10-17 10:31:50 +02:00
VERSION [RELEASE] Released version 2.3-dev7 2020-10-17 10:31:50 +02:00

README 

The HAProxy documentation has been split into a number of different files for
ease of use.

Please refer to the following files depending on what you're looking for :

  - INSTALL for instructions on how to build and install HAProxy
  - BRANCHES to understand the project's life cycle and what version to use
  - LICENSE for the project's license
  - CONTRIBUTING for the process to follow to submit contributions

The more detailed documentation is located into the doc/ directory :

  - doc/intro.txt for a quick introduction on HAProxy
  - doc/configuration.txt for the configuration's reference manual
  - doc/lua.txt for the Lua's reference manual
  - doc/SPOE.txt for how to use the SPOE engine
  - doc/network-namespaces.txt for how to use network namespaces under Linux
  - doc/management.txt for the management guide
  - doc/regression-testing.txt for how to use the regression testing suite
  - doc/peers.txt for the peers protocol reference
  - doc/coding-style.txt for how to adopt HAProxy's coding style
  - doc/internals for developer-specific documentation (not all up to date)