Comment 20 for bug 270046

The problem seems to be occurring in the prepareuser function of /usr/lib/cups/backend/cups-pdf. Specifically, the following check fails to correctly identify the presence of the user output directory (line 338 of cups-pdf.c):
  if (stat(dirname, &fstatus) || !S_ISDIR(fstatus.ts_mode))

Using up-to-date Ubuntu 8.10 with a clean install of cups and cups-pdf with default config files (i.e. purge and reinstall). Package versions:
  cups: 1.3.9-2ubuntu7
  cups-pdf: 2.4.8-1ubuntu1

Permissions on $HOME and ~/PDF/ both 700, which causes cups-pdf to fail:
  mathew@host:~/PDF$ ls -la
  total 8
  drwx------ 2 mathew mathew 4096 2009-03-13 11:25 .
  drwx------ 68 mathew mathew 4096 2009-03-13 11:16 ..

It appears that AppArmor is preventing the stat and S_ISDIR function calls (from sys/stat.h) from correctly determining the existence of the ~/PDF/ output directory. This is despite the AppArmor profile /etc/apparmor.d/usr.sbin.cupsd granting cups-pdf read/write access to that directory (lines 141-142 of usr.sbin.cupsd):
  @{HOME}/PDF/ rw,
  @{HOME}/PDF/* rw,

When prepareuser fails to find the ~/PDF/ directory, it then tries to (re)create it, which causes cups-pdf to fail as it doesn't (and shouldn't) have write access directly in $HOME.
Trying to print, e.g. '$ lp -d PDF /tmp/test.txt' results in the following error message in /var/log/cups/cups-pdf_log (originating from the prepareuser function):
  Fri Mar 13 12:57:45 2009 [ERROR] failed to create user output directory (/home/mathew/PDF)

The following also appears in /var/log/syslog:
  Mar 13 12:57:45 host kernel: [11411.156535] type=1503 audit(1236902265.708:18): operation="capable" name="dac_override" pid=5562 profile="/usr/lib/cups/backend/cups-pdf"
  Mar 13 12:57:45 host kernel: [11411.156549] type=1503 audit(1236902265.708:19): operation="capable" name="dac_read_search" pid=5562 profile="/usr/lib/cups/backend/cups-pdf"

If the prepareuser function is modified so that it doesn't check for the existence of the output directory, and simply return(s) 0; whenever it is called, cups-pdf works as expected. The unmodified version of cups-pdf will work when either AppArmor is not running, or $HOME is given permissions 701, with ~/PDF/ still having 700 permissions.