Bug#602306: update-notifier-common: segmentation fault

[Per Cederqvist <cederp@opera.com>]

I can reproduce this in Debian 7.2, like this:

 [1] $ sudo apt-get update
     [ lots of output ]
 [2] $ /usr/lib/update-notifier/apt-check;echo
     0;0
 [3] $ sudo touch /etc/apt/sources.list.d/foo.list
 [4] $ sudo chmod 600  /etc/apt/sources.list.d/foo.list
 [5] $ /usr/lib/update-notifier/apt-check;echo
     E: Error: Opening the cache (E:Opening
/etc/apt/sources.list.d/foo.list - ifstream::ifstream (13: Permission
denied), E:The list of sources could not be read., E:The package lists
or status file could not be parsed or opened.
 [6] $ sudo apt-get update
     [ lots of output ]
 [7] $ /usr/lib/update-notifier/apt-check;echo
     Segmentation fault (core dumped)
 [8] $ sudo chmod 644  /etc/apt/sources.list.d/foo.list
 [9] $ /usr/lib/update-notifier/apt-check;echo
     0;0
[10] $ sudo rm  /etc/apt/sources.list.d/foo.list
[11] $ /usr/lib/update-notifier/apt-check;echo
     0;0

In step 2 I have a system where the apt-check command works.

Steps 3 and 4 creates a file that is unreadable by the current user.

Step 5 shows apt-check printing an error message. (This isn't pretty, as
it contains no newlines, but it works.)

In step 6, I run apt-get update. Afterwards, in step 7, the apt-check
command no longer gives an error message. Instead, it crashes.

Step 8 and 9 shows that setting the permissions so that the file
is readable is enough to make apt-check work.

Step 10 and 11 shows that removing the unreadable file also
makes apt-cehck work. (This actually works even if you skip
step 8 and 9 as well.)

Yours,

    /ceder