locking problems with 2.1.9

[Peter Krotkov]

On Fri, 8 Nov 2002, Lawrence Greenfield wrote:

>    Date: Fri, 8 Nov 2002 11:04:32 -0500 (EST)
>    From: Peter Krotkov <pete at wookie.oit.umass.edu>
> [...]
>    22335:  imapd -s
>     ff09b3bc read     (0, 1c4bc8, 6f5)
>     0008e8c8 sock_read (0, 1c4bc8, 6f5, 8e8a0, 18edf8, 1) + 28
>     0008d670 BIO_read (1bd090, 1c4bc8, 6f5, 1c32a8, 1bccf0, 0) + d0
>     0007dec8 ssl3_read_n (5, 2010, 2010, 191b, 0, 0) + 148
>     0007e140 ssl3_get_record (1bb7e0, 1bccf0, 0, 0, 23138, ff0941d8) + 1e0
>     0007e8d4 ssl3_read_bytes (1bb7e0, 17, 1aa610, 1000, 0, 1bccf0) + 1d4
>     0007c6e8 ssl3_read (1bb7e0, 1aa610, 1000, 7c6a0, 19a1ac, 0) + 48
>     0006e730 SSL_read (1bb7e0, 1aa610, 1000, 1, ff0bd194, ffbec4b8) + 70
>     00060524 prot_fill (ffffffff, 0, 1000, 19cfb0, ffbec7b8, 1) + 340
>     00060d8c prot_read (0, ffbec7b8, 1000, 19cfb0, 1, ffbec7b8) + 6c
>     00050894 message_copy_strict (0, 19cfb0, 8008c, ffffeff8, 1a17a8, ff09c648) + 64
>     00044584 append_fromstream (ffbed830, 1a17a8, 9408c, 3cbce214, 1d0520, 1) + 14c
>
> This one looks like the one that's actually having the problem. If you
> kill this process, everything will return to normal.
>
> What caused this? Well, prot_fill() isn't suppose to call SSL_read if
> SSL_read is going to block. Unfortunately, it doesn't succeed in this
> case.
>
> Really, we should put the SSL socket into non-blocking mode and have
> some additional logic to make sure this doesn't happen. Since the prot
> layer itself is (generally) blocking, it's not totally trivial and we
> haven't done the work.
>
> Finally, there's the larger issue that we lock the mailbox during an
> APPEND which is a Bad Idea, since a client can be arbitrarily slow
> uploading data and thus creates a DoS for other clients. Avoiding this
> isn't probably that hard (the staging code used by lmtpd can probably
> be adapted by imapd) but we haven't done it, either.
>
> At the very least, I'd appreciate it if you open a bug on the SSL
> issue and include the backtrace on bugzilla.andrew.cmu.edu.
>
> Larry
>

Larry,

Thank your your time and energies for investigating the problem.  I will
open a bug for the SSL issue along with a backtrace.

Prior to a code fix to address the problems you observed, do you think it
would be unreasonable to configure master so that imaps is not offered?
We could revert to running stunnel for ssl support and then take our
chances with clients that initiate starttls. Our client base has become
quite accustomed to the overall reliability of cyrus and would go
ballistic with even an occasional imapd/lmtpd going bonkers :-}.

Many thanks,

Pete