[Dovecot] Calling dovecot-lda from within Antispam pipe script (bash) seems to have no effect

[Ben Morrow]

At  1PM -0400 on 21/06/13 you (Ben Johnson) wrote:
> On 6/20/2013 10:00 PM, Bob Miller wrote:
> > 
> >> It really boils-down to the fact that I can call the following on the
> >> command-line and it functions as expected:
> >>
> >> su vmail -c '/usr/lib/dovecot/deliver -a "sa-training at example.com" -d
> >> "sa-training at example.com" -m "Training.SPAM" -p
> >> "/tmp/sendmail-msg-25794.txt"'
> >>
> >> Yet, when I attempt to do the exact same thing from within the pipe
> >> script that Dovecot Antispam calls, I receive exit code 75 from
> >> deliver/dovecot-lda and absolutely nothing is logged, with exception of
> >> the information of which I'm already aware (logged to syslog).

Can you change lda to always log to syslog? It's possible you're not
seeing any logs because lda doesn't have permission to write to the log
files.

> >> I am echo-ing $(whoami) just before calling "deliver" within the pipe
> >> script and the output is "vmail". So, it's not as though the vmail user
> >> somehow lacks the permissions required to send via dovecot-lda.
> > 
> > There are two things that came to mind when I read your mail yesterday.
> > They are the first things I check for when my commands work and my
> > scripts don't.  
> > 
> > The first is $PATH, I have found innumerable times when a script
> > wouldn't run it was because it wasn't running with a fully loaded $PATH
> > variable, and this is especially true if you are launching your script
> > from cron.  To work around this I either put a PATH= at the top of the
> > script, or I run the script as an argument to bash instead of using the
> > executable bit (ie `bash /path/to/script.sh` instead of `./script.sh`)
> > so the path is retained from the shell.  I decided against mentioning
> > this yesterday because I noted you only used full paths in your script,
> > which should also work to avoid this problem.
> 
> All excellent insights.
> 
> You can see the PATH value in my previous message on this subject (from
> a few minutes ago); it matches the value that I see as "root" when I
> print the PATH within the shell. So, that seems okay.
> 
> Also, I took your good advice and eliminated the potential for the vmail
> user's shell choice (which happens to be /bin/sh, *not* /bin/bash)

Are you on a system where they are different?

> to
> affect the script's behavior. To do this I modified my antispam
> configuration directives as such:
> 
>   antispam_pipe_program = /bin/bash

It's generally better to write scripts in portable (or POSIX, at least)
Bourne shell, rather than relying on features of particular shells.

>   antispam_pipe_program_args = /usr/bin/sa-learn-pipe.sh
>   antispam_pipe_program_spam_arg = --spam
>   antispam_pipe_program_notspam_arg = --ham
> 
> Unfortunately, this change doesn't change the result at all; the call to
> "deliver" still exits with status code 75.
> 
> > The other thing I didn't mention was the permissions on the path
> > to /usr/lib/dovecot/deliver (or any other path, really).  Directories
> > with no world read/execute can prevent scripts from using files beneath
> > them if they don't have permissions on each directory level in the path.
> > I didn't mention this yesterday because you said you ran the script as
> > vmail.  However, looking at your "su vmail -c" command, I remember some
> > times when "su postrgres -c" didn't work when "su - postrgres" then
> > running the command did.
> 
> I have tried using "su vmail -c [...]", as well as "su vmail" and then
> pasting the command into the shell. Both yield the same result.

Have you checked the group rights are the same in both cases? Is there
any sort of MAC framework (SELinux or something similar) involved here?

> Also, there's no question that the vmail user is able to execute
> dovecot-adm; if he weren't, then a) pasting the command into the shell
> wouldn't work (and this does work), and b) I wouldn't be receiving exit
> status code 75, which is unique to dovecot-adm (I assume that I'd
> receive a more generic code, like 1, if it was a permissions problem).

75 is a standard exit code from <sysexits.h> indicating temporary
failure. Mail delivery programs need to be careful to distinguish
between temporary and permanent failure, so they nearly always use the
appropriate exit code.

> 
> > Probably neither of these will be useful to you, but I mention them in
> > hope that they trigger and idea or set you on an investigative path that
> > proves helpful...
> 
> Any help at all is useful! I really appreciate the time and thought you
> put into your posts. I wish I felt closer to a solution... :(
> 
> Please do reply if you have any additional thoughts. I'm at my wit's end
> here!

As I believe someone else has already mentioned, the big hammer of
strace is probably the most straightforward next step.

Ben