Bug#732746: apt: Empty /etc/apt/preferences file is not allowed

[Michael Vogt <mvo@debian.org>]

On Fri, Dec 20, 2013 at 11:51:35PM +0000, Will Marler wrote:
> Package: apt
> Version: 0.9.7.9+deb7u1
> Severity: normal

Thanks for your bugreport.

[..] 
> The bug can be reproduced quite simply by putting a single comment in /etc/apt/preferences. 
> For example:
> # This file is maintained by Puppet. Contents will be overwritten.
> 
> When running apt-get, the output will be:
> "E: Unable to parse package file /etc/apt/preferences (1)"
[..]
> It's clear that apt-get isn't checking the validity of the text following the "Package:" line, so
> why is it a requirement that the "Package:" line be present at all? 
[..]

I can reproduce the issue here and I agree that the current behavior
is confusing. Attached a patch with testcase that makes the parser
more relaxed. Feedback welcome.

Cheers,
 Michael

>From 75ab11ae3880530c5354cc90c8d1ff0998f8146b Mon Sep 17 00:00:00 2001
From: Michael Vogt <mvo@debian.org>
Date: Sat, 21 Dec 2013 18:50:03 +0100
Subject: [PATCH] make /etc/apt/preferences parser deal with comment only
 sections

---
 apt-pkg/policy.cc                            |  4 ++++
 apt-pkg/tagfile.cc                           | 11 ++++++++--
 test/integration/test-bug-732746-preferences | 32 ++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100755 test/integration/test-bug-732746-preferences

diff --git a/apt-pkg/policy.cc b/apt-pkg/policy.cc
index 0a06cc6..d0f9744 100644
--- a/apt-pkg/policy.cc
+++ b/apt-pkg/policy.cc
@@ -405,6 +405,10 @@ bool ReadPinFile(pkgPolicy &Plcy,string File)
    PreferenceSection Tags;
    while (TF.Step(Tags) == true)
    {
+      // can happen when there are only comments in a record
+      if (Tags.Count() == 0)
+         continue;
+
       string Name = Tags.FindS("Package");
       if (Name.empty() == true)
 	 return _error->Error(_("Invalid record in the preferences file %s, no Package header"), File.c_str());
diff --git a/apt-pkg/tagfile.cc b/apt-pkg/tagfile.cc
index e0802e3..bef3c76 100644
--- a/apt-pkg/tagfile.cc
+++ b/apt-pkg/tagfile.cc
@@ -259,7 +259,12 @@ bool pkgTagSection::Scan(const char *Start,unsigned long MaxLength)
    TagCount = 0;
    while (TagCount+1 < sizeof(Indexes)/sizeof(Indexes[0]) && Stop < End)
    {
-       TrimRecord(true,End);
+      TrimRecord(true,End);
+
+      // this can happen when TrimRecord trims away the entire Record
+      // (e.g. because it just contains comments)
+      if(Stop == End)
+         return true;
 
       // Start a new index and add it to the hash
       if (isspace(Stop[0]) == 0)
@@ -273,7 +278,9 @@ bool pkgTagSection::Scan(const char *Start,unsigned long MaxLength)
       if (Stop == 0)
 	 return false;
 
-      for (; Stop+1 < End && Stop[1] == '\r'; Stop++);
+      for (; Stop+1 < End && Stop[1] == '\r'; Stop++)
+         /* nothing */
+         ;
 
       // Double newline marks the end of the record
       if (Stop+1 < End && Stop[1] == '\n')
diff --git a/test/integration/test-bug-732746-preferences b/test/integration/test-bug-732746-preferences
new file mode 100755
index 0000000..b31f98a
--- /dev/null
+++ b/test/integration/test-bug-732746-preferences
@@ -0,0 +1,32 @@
+#!/bin/sh
+set -e
+
+TESTDIR=$(readlink -f $(dirname $0))
+. $TESTDIR/framework
+setupenvironment
+configarchitecture 'i386'
+
+insertinstalledpackage 'bar' 'i386' '1.0'
+
+cat > rootdir/etc/apt/preferences << EOF
+# random test comment header
+
+# commented out by puppy^Wpuppet
+#Package: foo
+#Pin: origin "ftp.debian.org"
+#Pin: 800
+
+Package: bar
+Pin: version 1.0
+Pin-Priority: 700
+
+#Package: bar
+#Pin: version 1.0
+#Pin: 800
+EOF
+
+testequal "Reading package lists...
+Building dependency tree..." aptget check
+
+msgtest "Ensure policy is applied"
+aptcache policy bar|grep -q "*** 1.0 700" && msgpass || msgfail
-- 
1.8.3.2