ghostscript: ensure update of cups-filter

[Mauricio Faria de Oliveira]

[Impact]

 * After an update of ghostscript but not cups-filters
   users may hit errors printing PDF files (LP#1828401).

 * This is possible as Landscape does not consider the
   -security pocket (has both ghostscript/cups-filters)
   but rather USN notices and ghostscript had a notice [0].
   The regression on cups-filters was identified later,
   and doesn't warrant a USN notice.

 * So, to ensure that ghostscript and cups-filters are
   both updated, add a versioned 'Breaks:' relationship
   to ghostscript for older cups-filters versions which
   are not yet fixed.

   Per Debian Policy [1]:

     """
     Normally a Breaks entry will have an “earlier than” version clause;
     such a Breaks is introduced in the version ... [that] reveals a bug
     in earlier versions of the broken package ...

     This use of Breaks will inform higher-level package management tools
     that the broken package must be upgraded before the new one.
     """

 * A versioned 'Depends:' relationship is not possible
   as ghostscript doesn't depend on cups-filters, thus
   it's possible to have ghostscript installed without
   cups-filters at all.

 * This doesn't fix the current situation with Landscape
   and USNs so this same problem might still occur again,
   but at least it is already in place on future updates.

[Test Case]

 * Install cups-filters version without fix for LP#1828401:
   1.20.2-0ubuntu3 in Bionic, and 1.8.3-2ubuntu3.4 in Xenial.

 * Update ghostscript to/later than fix for CVE-2019-3839-1/-2
   9.26~dfsg+0-0ubuntu0.18.04.9 in Bionic / .16.04.9 in Xenial.

 * Notice it does _not_ update cups-filters to version with fix:
   1.20.2-0ubuntu3.1 in Bionic, and 1.8.3-2ubuntu3.5 in Xenial.

 * $ wget -O ppd-with-pdf-support.ppd \
     'http://www.openprinting.org/ppd-o-matic.php?driver=hl7x0&printer=Brother-HL-1020&show=1'

 * $ wget -O dummy.pdf \
     https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf

 * $ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
   ...
   Filetype: PDF
   GPL Ghostscript 9.26: Unrecoverable error, exit code 1
   Process is dying with "Unable to determine number of pages, page count: -1
   ", exit stat 3
   ...

 * Note it's broken.

 * Install ghostscript (test) packages with the relationships
   'Breaks: cups-filters (<< 1.20.2-0ubuntu3.1)' in Bionic or
   'Breaks: ..., cups-filters (<< 1.8.3-2ubuntu3.5)' in Xenial.

 * Note it _does_ update cups-filters to version with fix.

 * $ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
   ...
   Filetype: PDF
   File contains 1 pages
   Starting renderer with command: <...>
   ...

 * Note it's now working.

[Regression Potential]

 * Low. This only causes an update to cups-filters to a version
   that fixes an already identified/resolved problem (LP#1828401),
   which is available in bionic- & xenial-updates since May 2019.

[Other Info]

 * This is only required in Xenial and Bionic.

 * Trusty doesn't have the ghostscript update that causes the problem.

 * Disco/Eoan have the cups-filters fix that it requires (1.22.5+).

[Links]

[0] https://usn.ubuntu.com/3970-1/
[1] https://www.debian.org/doc/debian-policy/ch-relationships.html#packages-which-break-other-packages-breaks

[Mauricio Faria de Oliveira (mfo)]

Testing on Bionic
---

Files)

$ wget -O ppd-with-pdf-support.ppd 'http://www.openprinting.org/ppd-o-matic.php?driver=hl7x0&printer=Brother-HL-1020&show=1'

$ wget -O dummy.pdf https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf

Test 0) Before updating ghostscript or cups-filters

$ dpkg -s cups-filters ghostscript | grep ^Version:
Version: 1.20.2-0ubuntu3
Version: 9.26~dfsg+0-0ubuntu0.18.04.8

$ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
...
Filetype: PDF
File contains 1 pages
Starting renderer with command: <...>
...

Test 1) After updating ghostscript (not cups-filters)

$ dpkg -s cups-filters ghostscript | grep ^Version:
Version: 1.20.2-0ubuntu3
Version: 9.26~dfsg+0-0ubuntu0.18.04.11

$ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
...
Filetype: PDF
GPL Ghostscript 9.26: Unrecoverable error, exit code 1
Process is dying with "Unable to determine number of pages, page count: -1
", exit stat 3
...

Test 2) Checking before updating ghostscript with test package (thus cups-filters too)

Checking update of cups-filters with apt:

$ sudo apt install --dry-run ghostscript
...
The following packages will be upgraded:
  cups-filters ghostscript libgs9 libgs9-common
...
Inst cups-filters [1.20.2-0ubuntu3] (1.20.2-0ubuntu3.1 Ubuntu:18.04/bionic-updates, Ubuntu:18.04/bionic-security [amd64])
Inst ghostscript [9.26~dfsg+0-0ubuntu0.18.04.11] (9.26~dfsg+0-0ubuntu0.18.04.11+test20191510b1 mfo-sf246942:18.04/bionic [amd64]) []
...

Checking update of cups-filters with apt-get:

$ sudo apt-get install --dry-run ghostscript
...
The following packages will be upgraded:
  cups-filters ghostscript libgs9 libgs9-common
...
Inst cups-filters [1.20.2-0ubuntu3] (1.20.2-0ubuntu3.1 Ubuntu:18.04/bionic-updates, Ubuntu:18.04/bionic-security [amd64])
Inst ghostscript [9.26~dfsg+0-0ubuntu0.18.04.11] (9.26~dfsg+0-0ubuntu0.18.04.11+test20191510b1 mfo-sf246942:18.04/bionic [amd64]) []
...

Test 3) After updating ghostscript with test package (thus cups-filters too)

$ dpkg -s cups-filters ghostscript | grep ^Version:
Version: 1.20.2-0ubuntu3.1
Version: 9.26~dfsg+0-0ubuntu0.18.04.11+test20191510b1

$ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
...
Filetype: PDF
File contains 1 pages
Starting renderer with command: <...>
...

[Mauricio Faria de Oliveira (mfo)]

Testing on Xenial
---

Files)

$ wget -O ppd-with-pdf-support.ppd 'http://www.openprinting.org/ppd-o-matic.php?driver=hl7x0&printer=Brother-HL-1020&show=1'

$ wget -O dummy.pdf https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf

Test 0) Before updating ghostscript or cups-filters
$ dpkg -s cups-filters ghostscript | grep ^Version:
Version: 1.8.3-2ubuntu3.4
Version: 9.26~dfsg+0-0ubuntu0.16.04.8

$ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
...
Filetype: PDF
File contains 1 pages
Starting renderer with command: <...>
...

Test 1) After updating ghostscript (not cups-filters)

$ dpkg -s cups-filters ghostscript | grep ^Version:
Version: 1.8.3-2ubuntu3.4
Version: 9.26~dfsg+0-0ubuntu0.16.04.11

$ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
...
Filetype: PDF
GPL Ghostscript 9.26: Unrecoverable error, exit code 1
Process is dying with "Unable to determine number of pages, page count: -1
", exit stat 3
...

Test 2) Checking before updating ghostscript with test package (thus cups-filters too)

Checking update of cups-filters with apt-get and apt:

$ sudo apt-get install --dry-run ghostscript
...
The following packages will be upgraded:
  cups-filters cups-filters-core-drivers ghostscript libgs9 libgs9-common
...
Inst cups-filters [1.8.3-2ubuntu3.4] (1.8.3-2ubuntu3.5 Ubuntu:16.04/xenial-updates, Ubuntu:16.04/xenial-security [amd64])
Inst ghostscript [9.26~dfsg+0-0ubuntu0.16.04.11] (9.26~dfsg+0-0ubuntu0.16.04.11+test20191510b1 mfo-sf246942:16.04/xenial [amd64]) []
...

$ sudo apt install --dry-run ghostscript
...
The following packages will be upgraded:
  cups-filters cups-filters-core-drivers ghostscript libgs9 libgs9-common
...
Inst cups-filters [1.8.3-2ubuntu3.4] (1.8.3-2ubuntu3.5 Ubuntu:16.04/xenial-updates, Ubuntu:16.04/xenial-security [amd64])
Inst ghostscript [9.26~dfsg+0-0ubuntu0.16.04.11] (9.26~dfsg+0-0ubuntu0.16.04.11+test20191510b1 mfo-sf246942:16.04/xenial [amd64]) []
...

Test 3) After updating ghostscript with test package (thus cups-filters too)

$ dpkg -s cups-filters ghostscript | grep ^Version:
Version: 1.8.3-2ubuntu3.5
Version: 9.26~dfsg+0-0ubuntu0.16.04.11+test20191510b1

$ foomatic-rip -v --ppd ppd-with-pdf-support.ppd dummy.pdf
...
Filetype: PDF
File contains 1 pages
Starting renderer with command: <...>
...

[Mauricio Faria de Oliveira (mfo)]

Test packages used for verification in comments #1 and #2
built successfully on all architectures, ppa:mfo/sf246942 [1].

[1] https://launchpad.net/~mfo/+archive/ubuntu/sf246942

[Mauricio Faria de Oliveira (mfo)]

The approach to fix/deliver this is under discussion for a bit.
We'll move forward once that's more clearly defined.

[Mauricio Faria de Oliveira (mfo)]

After discussing this with Eric (slashd) and Marc (mdeslaur),
it seems like the Breaks: approach is indeed the way to go.

Nonetheless, it doesn't warrant an USN notice (security-only),
which is the bit that could make Landscape (problem trigger)
to pick up the new ghostscript fix then update cups-filters.

So, we agreed on likely folding this fix/update into another
SRU, as the impact to other audiences (non-Landscape) is small,
because both ghostscript/cups-filters are on -security pocket.

If other users are hit by this issue, we can sure enough
revisit that option and consider some form to deliver it.

cheers,
Mauricio

[Mauricio Faria de Oliveira (mfo)]

It looks like this wasn't needed in practice; marking as Won't Fix.