CUPS wrapper for Kyocera rastertokpsl

A wrapper for the CUPS rastertokpsl filter designed to prevent crashes of the original Kyocera filter when processing print jobs with long or non-ASCII titles.

Problem

Some versions of the Kyocera rastertokpsl filter use a fixed-size buffer to process the job title. Passing a long string or a string containing Cyrillic characters can cause a buffer overflow and result in the filter terminating unexpectedly:

*** buffer overflow detected ***: terminated

In the CUPS logs, this may look like:

PID 30752 (/usr/lib/cups/filter/rastertokpsl) crashed on signal 6

As a result, the job is not printed and the printer queue may enter the stopped state.

Solution

The wrapper intercepts the CUPS arguments before launching the original rastertokpsl.

Before passing the job title to the original filter, the wrapper:

• converts UTF-8 to ASCII;
• removes unsupported characters;
• limits the string length;
• uses print-job if the resulting string is empty.

The original binary is stored as:

/usr/lib/cups/filter/rastertokpsl.real

The wrapper is installed in its place:

/usr/lib/cups/filter/rastertokpsl

Installation

First, save the original filter:

sudo cp /usr/lib/cups/filter/rastertokpsl \
        /usr/lib/cups/filter/rastertokpsl.real

Create the wrapper file:

sudo nano /usr/lib/cups/filter/rastertokpsl

Contents:

#!/bin/bash

REAL="/usr/lib/cups/filter/rastertokpsl.real"

# Kyocera rastertokpsl uses the following arguments:
# $1 printer
# $2 job-id
# $3 title
# $4 copies
# $5 options

if [ "$#" -ne 5 ]; then
    echo "ERROR: rastertokpsl wrapper: expected 5 arguments, got $#" >&2
    exit 1
fi

printer="$1"
job_id="$2"
title="$3"
copies="$4"
options="$5"

# Convert the title to ASCII, remove unsupported characters,
# and limit its length to 20 characters.
safe_title="$(
    printf '%s' "$title" |
    iconv -f UTF-8 -t ASCII//TRANSLIT 2>/dev/null |
    LC_ALL=C tr -cd 'A-Za-z0-9' |
    tail -c 20
)"

[ -n "$safe_title" ] || safe_title="print-job"

# Pass the raster data through stdin.
exec "$REAL" \
    "$printer" \
    "$job_id" \
    "$safe_title" \
    "$copies" \
    "$options"

Set the appropriate permissions:

sudo chown root:root /usr/lib/cups/filter/rastertokpsl
sudo chmod 755 /usr/lib/cups/filter/rastertokpsl
sudo chmod 755 /usr/lib/cups/filter/rastertokpsl.real

Restart CUPS:

sudo systemctl restart cups

Verification

Make sure the original file is an executable binary:

file /usr/lib/cups/filter/rastertokpsl.real

The expected output should contain ELF ... executable.

Test printing a normal job:

lp -d PRINTER /tmp/test.pdf

Then test a job with a long title:

lp -d PRINTER \
   -t "Very long Cyrillic job title for testing" \
   /tmp/test.pdf

Check the queue status:

lpstat -p
lpstat -o

To enable verbose CUPS logging when needed:

sudo cupsctl --debug-logging
sudo tail -F /var/log/cups/error_log

After troubleshooting is complete:

sudo cupsctl --no-debug-logging

Restoring the Original Filter

To remove the wrapper and restore the original rastertokpsl:

sudo mv /usr/lib/cups/filter/rastertokpsl.real \
        /usr/lib/cups/filter/rastertokpsl

sudo systemctl restart cups

Limitations

The wrapper is designed for a specific Kyocera rastertokpsl interface that uses five arguments:

printer job-id title copies options

The 20 character limit was chosen as a conservative restriction for problematic filter versions. The exact size of the internal buffer depends on the specific rastertokpsl driver version and is not determined by CUPS itself.

Before installation, it is recommended to back up the original binary and check the driver version.

Repository Structure

Example repository structure:

cups-kyocera-rastertokpsl-fix/
├── README.md
└── rastertokpsl

The rastertokpsl file from the repository is installed to:

/usr/lib/cups/filter/rastertokpsl