dovecot - Aug 2012 - Possible mbox corruption if mail is saved with wrong Content-Length header (2.1.6)

One of our users likes to delete attachments from his mails. He is using
roundcube and we installed a plugin for that.

He reports that from time to time one of his mails gets corrupted (cut
off in the middle).

I could verify there is something wrong in the logs:

imap(x1234567): Error: Cached message size larger than expected (6796 > 2844)
imap(x1234567): Error: Corrupted index cache file
/net/mbx3/disc2/home/85/x1234567/Index/.imap/Sent/dovecot.index.cache: Broken
physical size for mail UID 5001
imap(x1234567): Error: read(/net/mbx3/disc2/home/85/x1234567/Mail/Sent) failed:
Input/output error (FETCH for mailbox Sent UID 5001)
imap(x1234567): Info: Disconnected: Internal error occurred. Refer to server log
for more information. [2012-08-23 00:00:49] in=1124145 out=1324791

I had a look at the plugin and it works by duplicating the message and
leaving out the attachment(s). The headers are also duplicated,
including Content-Length. I've fixed that in the plugin, (don't know yet
if it helps), but I think it shouldn't cause such breakage in dovecot.

# doveconf -n
# 2.1.6: /usr/local/dovecot/etc/dovecot/dovecot.conf
# OS: Linux 2.6.9-103.ELsmp i686 Red Hat Enterprise Linux AS release 4 (Nahant
Update 9)
doveconf: Warning: Dovecot was last started using
/usr/local/dovecot/etc/dovecot.conf, but this config is
/usr/local/dovecot/etc/dovecot/dovecot.conf
auth_master_user_separator = *
disable_plaintext_auth = no
doveadm_password = (hidden)
lda_mailbox_autocreate = yes
log_path = /dev/stderr
log_timestamp mail_location = mbox:~/Mail:INBOX=~/Mailbox:INDEX=~/Index
mail_plugins = " quota zlib mail_log notify virtual"
mdbox_rotate_size = 5 M
namespace {
  hidden = no
  inbox = yes
  location   prefix   separator = /
  type = private
} 
namespace {
  hidden = yes
  inbox = no
  list = children
  location = maildir:~/Maildir
  prefix = "#MD/"
  separator = /
  type = private
}
passdb {
  driver = pam
}
passdb {
  args = /usr/local/dovecot/etc/passwd.dovcot.master
  driver = passwd-file
  master = yes
}
plugin {
  acl = vfile
  mail_log_events = undelete mailbox_delete mailbox_rename mailbox_create
  mail_log_fields = uid box msgid size
  quota = fs:Disk quota
}
protocols = pop3 imap
service auth {
  client_limit = 4300
  user = root
}
service doveadm {
  inet_listener {
    port = 542
  }
}
service imap-login {
  inet_listener imap {
    address = 134.147.64.42
    port = 143
  }
  service_count = 0
}
service imap {
  drop_priv_before_exec = yes
  process_limit = 4096
  vsz_limit = 1 G
}
service pop3-login {
  inet_listener pop3 {
    address = 134.147.64.42
    port = 110
  }
  service_count = 0
}
service pop3 {
  drop_priv_before_exec = yes
  process_limit = 2048
  vsz_limit = 512 M
}
ssl = no
userdb {
  driver = passwd
}
protocol imap {
  mail_max_userip_connections = 50
  mail_plugins = " quota zlib mail_log notify virtual imap_quota
imap_zlib"
}

Thanks
Jost Krieger
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On 31.8.2012, at 11.42, Jost Krieger wrote:
> One of our users likes to delete attachments from his mails. He is using
> roundcube and we installed a plugin for that.
Does the plugin change the mbox file directly?
> imap(x1234567): Error: Cached message size larger than expected (6796 >
2844)
This looks like it does. Existing emails must not be changed, IMAP protocol
forbids it (and Dovecot internals don't support it either). The only safe
way to drop attachments is to assign a new UID for the mail, which basically
means saving a new message without attachments and deleting the old one. The
Content-Length header doesn't really have anything to do with this error.