Bug#689582: ExtractTar: 100 char long path names get truncated to 99 chars

[Mika Eloranta <mel_debian@ohmu.fi>]

Package: apt
Version: 0.9.7.5
Severity: important

Dear Maintainer,

When a data.tar.{gz,xz} contains a path name that is exactly
100 characters long, it will get truncated to 99 chars upon
extraction in ExtractTar::Go().

It seems in older gnu tar versions (pre-wheezy) the behavior
was more conservative and to use the 100 byte path field only
for path names less than 100 chars long, and to switch to
using long names already at 100 chars. In wheezy the
behavior seems to be different and path names of exactly
100 chars long can fill the whole reserved space in the tar
and then get truncated in ExtractTar::Go():

      // Grab the filename
      if (LastLongName.empty() == false)
         Itm.Name = (char *)LastLongName.c_str();
      else
      {
         Tar->Name[sizeof(Tar->Name)-1] = 0;
         Itm.Name = Tar->Name;
      }

Quick way to reproducing the problem using a generated dummy
deb package and "python-apt" is included as an attachment.

-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.2.0-3-amd64 (SMP w/11 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages apt depends on:
ii  debian-archive-keyring  2012.4
ii  gnupg                   1.4.12-4+b1
ii  libapt-pkg4.12          0.9.7.5
ii  libc6                   2.13-35
ii  libgcc1                 1:4.7.1-7
ii  libstdc++6              4.7.1-7

apt recommends no packages.

#! /usr/bin/python
import os
import apt_inst

paths = []
for i in range(98,103):
	path = ("%03d" % i).ljust(i,"x")
        file(path, "w")
        paths.append(path)

assert not os.system("tar zcf data.tar.gz %s" % " ".join(paths))
file("control.tar.gz", "w")
file("debian-binary", "w")
assert not os.system("ar cr test.deb data.tar.gz control.tar.gz debian-binary")

def cb(a, b):
        print "%3d %s"  % (len(a.name), a.name)

apt_inst.DebFile(file("test.deb", "rb")).data.go(cb)