[Debconf-devel] Bug#745504: debconf: skip paging on terminals with 2 rows or less

[Apollon Oikonomopoulos]

Package: debconf
Version: 1.5.52
Severity: normal

Dear Maintainer,

The code in Debconf::FrontEnd::Teletype's display_nowrap silently
assumes that the display has more than 2 rows. On a terminal with 2 rows
or less, display_nowrap enters an endless loop, since no actual text
line is ever displayed, only the prompt itself.

I admit this is an extreme corner-case, but the following scenario can bring a
whole system down:

 1. Launch a debconf-using application in a two-row terminal
 2. Kill the parent process while debconf is paging

On the next input or signal, the debconf process will spin
uncontrollably; reading from STDIN will return immediately due to the
broken pipe and as prompt() does not check for errors while reading the
response, it will try to display_nowrap("\n") unconditionally, which in
turn will call prompt() recursively ad infinitum (or until the system's
memory is exhausted).

The attached patch fixes the issue.

Regards,
Apollon

-- System Information:
Debian Release: jessie/sid
  APT prefers testing
  APT policy: (500, 'testing'), (500, 'stable'), (90, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.13-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=el_GR.UTF-8, LC_CTYPE=el_GR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages debconf depends on:
ii  perl-base  5.18.2-2+b1

Versions of packages debconf recommends:
ii  apt-utils     1.0.1
ii  debconf-i18n  1.5.52

Versions of packages debconf suggests:
ii  debconf-doc                1.5.52
ii  debconf-utils              1.5.52
ii  libgtk2-perl               2:1.249-2
ii  libnet-ldap-perl           1:0.6200+dfsg-1
pn  libqtcore4-perl            <none>
pn  libqtgui4-perl             <none>
ii  libterm-readline-gnu-perl  1.24-1
ii  perl                       5.18.2-2+b1
ii  whiptail                   0.52.15-3+b1

-- debconf-show failed

-- 
Apollon Oikonomopoulos               apollon at skroutz.gr
Skroutz S.A.                          http://skroutz.gr
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