I'm unable to trigger this bug when running the test case on trusty, even though the same code is there. I also tried adjusting the sleep.
-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to cyrus-sasl2 in Ubuntu. https://bugs.launchpad.net/bugs/997217 Title: salsauthd maxes cpu Status in cyrus-sasl2 package in Ubuntu: Fix Released Status in cyrus-sasl2 source package in Precise: Won't Fix Status in cyrus-sasl2 source package in Trusty: Triaged Status in cyrus-sasl2 source package in Xenial: Triaged Bug description: [Impact] The rimap authentication mechanism in saslauthd can hit a condition where it will start spinning and using all available CPU. This condition can be easily encountered when an authentication is happening and the imap service is being restarted. Furthermore, the saslauthd child process that picked up that authentication request and that is spinning now won't be reaped nor can it service further requests. If all children are left in this state, the authentication service as a whole won't be working anymore. [Test Case] This test can be performed in a LXD or VM. * install the needed packages. mail-stack-delivery is used to have an imap server available on localhost that needs no further configuration. Accept the defaults for all debconf prompts: sudo apt update sudo apt install sasl2-bin mail-stack-delivery * set the password "ubuntu" for the ubuntu user echo ubuntu:ubuntu | sudo chpasswd * start saslauthd like this, with just one child: sudo /usr/sbin/saslauthd -a rimap -O localhost -r -n 1 * restart dovecot sudo service dovecot restart * test saslauthd authentication: $ sudo testsaslauthd -u ubuntu -p ubuntu 0: OK "Success." * Now let's break it. In one terminal watch the output of top: top * in another terminal, run the following: sudo testsaslauthd -u ubuntu -p ubuntu & sleep 1; sudo service dovecot stop * observe in the "top" terminal that saslauthd is consuming a lot of cpu. If that's not happening, try starting dovecot again and adjusting the sleep value in the previous test command. * repeat the authentication request. Since the only saslauthd child is now spinning, this will block: $ sudo testsaslauthd -u ubuntu -p ubuntu <blocks> [Regression Potential] * discussion of how regressions are most likely to manifest as a result of this change. * It is assumed that any SRU candidate patch is well-tested before upload and has a low overall risk of regression, but it's important to make the effort to think about what ''could'' happen in the event of a regression. * This both shows the SRU team that the risks have been considered, and provides guidance to testers in regression-testing the SRU. [Other Info] * Anything else you think is useful to include * Anticipate questions from users, SRU, +1 maintenance, security teams and the Technical Board * and address these questions in advance [Original Description] sasl2-bin version 2.1.24~rc1.dfsg1+cvs2011-05-23-4ubuntu contains a bug that causes heavy cpu utilization, impacting normal operation of one of our mail servers following an upgrade to Ubuntu 12.04. We are running the daemon with the following options: /usr/sbin/saslauthd -a rimap -O our.imap.server -r -m /var/spool/postfix/var/run/saslauthd -n 5 We noticed that users were unable to send mail and that the saslauthd processes were using approximately 100% of each cpu core. An strace of one of the runaway process showed that it was stuck in the following behaviour: select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 select(9, [8], NULL, NULL, {0, 0}) = 1 (in [8], left {0, 0}) read(8, "", 940) = 0 ..... with further inspection showing that the file descriptor in question was a socket connected to our imap server in CLOSE_WAIT. Browsing saslauthd/auth_rimap.c in the source package for sasl2-bin, we came across the following code, repeated in two locations: while( select (fds, &perm, NULL, NULL, &timeout ) >0 ) { if ( FD_ISSET(s, &perm) ) { ret = read(s, rbuf+rc, sizeof(rbuf)-rc); if ( ret<0 ) { rc = ret; break; } else { rc += ret; } } } It looks like this loop is expected to run until a read error is encountered or the timeout of 1 second is reached. There is no test to check that 0 bytes were read, indicating that the connection was closed by the remote peer. Since select() will immediately return the size of the set of the partially closed descriptor (1, which is >0), and calls to read() will always yield 0 bytes, there's the potential for execution to get stuck in this non blocking loop and I'm presuming that that's what's happening here. We've not performed any further analysis to prove that this is really what's happening but if my intuition is correct then our IMAP server (an nginx imap proxy) most liklely closes the connection at an unexpected time under as yet undetermined conditions. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cyrus-sasl2/+bug/997217/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
