dovecot-2.2.13 running on Solaris-10, app 5000 concurrent connections, and a pretty standard config where passdb is set up with driver = pam.

We have had some situations where an auth-worker gets into a loop, the load on the server rises and the auth-master seems blocked untill finally no new imap nor pop session are accepted. A 'doveadm reload' restores normal operations.

With debug logging enabled we are observing this: auth: Debug: pam(,10.10.30.33,<7WMu3UkEGQCBsR4h>): cache miss auth-worker(24556): Debug: pam(,10.10.30.33): lookup service=dovecot auth-worker(24556): Debug: pam(,10.10.30.33): #1/1 style=2 msg=Please enter user name: ... auth-worker(24556): Debug: pam(,10.10.30.33): #1/1 style=2 msg=Please enter user name: etc etc

After some time dovecot only logs Warning: Auth process not responding, delayed sending initial response (greeting) Disconnected: Auth process broken (disconnected before auth was ready, waited 26 secs)

'truss -wall -aep PID' on the looping auth-worker shows the loop: 0.0757 write(2, 0x080AE0C0, 71) = 71 0101 2 4 5 5 6 p a m ( , 1 0 . 1 0 . 3 0 . 3 3 ) : # 1 / 1 s t y l e = 2 m s g = P l e a s e e n t e r u s e r
n a m e : \n 0.0826 write(2, 0x080AE0C0, 71) = 71 0101 2 4 5 5 6 p a m ( , 1 0 . 1 0 . 3 0 . 3 3 ) : # 1 / 1 s t y l e = 2 m s g = P l e a s e e n t e r u s e r
n a m e : \n

The host at 10.10.30.33 is running RoundCube for app 1000 concurrent users. This problem started after we provided our users RoundCube, and every time we end up in this stuck situation, it is the RoundCube-server making the connections where the username has zero length. I am unable to reproduce how RoundCube puts dovecot into this mess.

With the enclosed patch installed, the loop terminates and normal operation are restored immediately: auth: Debug: pam(,10.10.30.33,<Q8kV6AEFYwCBsR4h>): cache miss auth-worker(18658): Debug: pam(,10.10.30.33): lookup service=dovecot auth-worker(18658): Debug: pam(,10.10.30.33): #1/1 style=2 msg=Please enter user name: auth-worker(18658): Fatal: NO USER? auth-worker(18658): Error: Raw backtrace: 0xfef0798c -> 0xfef06d3b -> 0x807ca6e -> 0xfecc460e -> 0xfecc1d1e -> 0xfe3c0af4 -> 0xfecc2608 -> 0xfecc27f1 -> 0x807cc5e -> 0x807d162 -> 0x807d310 -> 0x8069ca1 -> 0x806ab72 -> 0x806aeec -> 0xfef1e866 -> 0xfef2001c -> 0xfef1e9ff -> 0xfef1e956 -> 0xfeeb0172 -> 0x8071bf2 -> 0x805a650 auth: Error: auth worker: Aborted PASSV request for : Worker process died unexpectedly

I think however, that the pam driver should not have been initiated when the username has zero length, definitely there is nobody around to answer the prompt for a username ...

hmk