[Bug 236605] mail/sendmail: additional blacklisting for frequent useless connections [patch]

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236605

            Bug ID: 236605
           Summary: mail/sendmail: additional blacklisting for frequent
                    useless connections [patch]
           Product: Ports & Packages
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: Individual Port(s)
          Assignee: dinoex at FreeBSD.org
          Reporter: freebsd at oldach.net
          Assignee: dinoex at FreeBSD.org
             Flags: maintainer-feedback?(dinoex at FreeBSD.org)

Created attachment 202938
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=202938&action=edit
patch

In my maillog, I often observe hosts frequently contacting my sendmail without
issuing any reasonable command, like this for example:

Mar 17 03:02:04 nuc sm-mta[98005]: x2H21q18098005: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:02:15 nuc sm-mta[98132]: x2H2278J098132: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:02:27 nuc sm-mta[98166]: x2H22JfW098166: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:02:36 nuc sm-mta[98167]: x2H22SXD098167: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:02:44 nuc sm-mta[98168]: x2H22aUN098168: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:02:53 nuc sm-mta[98169]: x2H22if3098169: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:03:01 nuc sm-mta[98170]: x2H22rvQ098170: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:03:09 nuc sm-mta[98176]: x2H231fG098176: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:03:17 nuc sm-mta[98177]: x2H239Q3098177: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4
Mar 17 03:03:26 nuc sm-mta[98211]: x2H23I3V098211: [221.227.107.69] did not
issue MAIL/EXPN/VRFY/ETRN during connection to IPv4

In some cases I have observed hundreds of such connection attempts before
giving up.

As we have blacklisting in the port, I was thinking to use that for calming
down such servers. However it appears this particular logic is not in the
blacklisting patch set yet.

The attached patch implements this. Admittedly it's kind of hackish as the "did
not issue" message is emitted only when sendmail's input file descriptor is
already closed, so we cannot use it for hand-over to blacklist() in the same
way as it's done for the other blacklist() calls. Therefore I'm dup()ing the
input fd early in the command loop for use by blacklist() and close the dup'ed
fd later.

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