Virus Screening with the Conversion Channel


Virus scanners are most readily interfaced to PMDF via the conversion channel. Sites can wrap their virus scanners in a routine or procedure which conducts the scan in much the same way as if it were to run from the command line.

When the scan is conducted, the following decisions are to be considered:

  1. If the scan indicates that there are no viruses then the message part retains its original content and is reincorporated into the main message and delivered to its final destination.

  2. If the scan implies that there is a virus in the message part, then either

    (a) sanitize the infected message part.

    or

    (b) discard the infected message part and substitute a text message of some sort (e.g., "warning virus detected, infected part removed").

    or

    (c) return the message as undeliverable.

Invoking your Procedures To invoke conversion procedures, use the CONVERSION mapping table in the PMDF_MAPPING_FILE to tell PMDF that the message should take a pass through the conversion channel. When the message passes through the conversion channel, instructions as to what commands to execute are to be laid out in the PMDF_CONVERSION_FILE.

The PMDF_CONVERSION_FILE is /pmdf/table/conversions on UNIX
The PMDF_MAPPING_FILE is /pmdf/table/mappings on UNIX

The PMDF_CONVERSION_FILE is PMDF_TABLE:CONVERSIONS. on VMS
The PMDF_MAPPING_FILE is PMDF_TABLE:MAPPINGS. on VMS

A typical CONVERSION table in the PMDF_MAPPING_FILE reads:

!
CONVERSION

 IN-CHAN=foo;OUT-CHAN=bar;CONVERT            Yes

!
! Make all messages going from channel 'foo' to channel 'bar' take a
! detour through the conversion channel.
!

... and a typical entry in the PMDF_CONVERSION_FILE reads:
!
in-channel=*; in-type=APPLICATION; in-subtype=octet-stream;
  parameter-symbol-0=NAME; parameter-copy-0=*;
  dparameter-symbol-0=FILENAME; dparameter-copy-0=*;
  message-header-file=2; original-header-file=1;
  override-header-file=1; override-option-file=1;
  command="the-command-to-run-the-converter-script"

!
! Message parts which have a MIME-type  of "APPLICATION/octet-stream",
! should be processed by the "converter-script" command.
!

Scripting Samples

Sample scripts for integrating VSWEEP (and other virus scanners) with the conversion channel are available for download. VMS samples are at (1), (2), (3) (4) while the UNIX samples are in a compressed tar file here.

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