Restore dpkg::chroot-directory functionality

If we call dpkg inside a chroot we have to ensure that the temporary
directory we construct to call dpkg --recursive is inside the chroot and
that we strip the path to the chroot from the directory name we pass to
dpkg.

Note that the added test succeeds before and (hopefully) after as we
can't really chroot here or fiddle with the needed settings as we are
already setting up apt to work with a quasi-chroot. The test perhaps
helps in ensuring we don't break it too much in the future though.

(Broken five years (and one day) ago this seems to have an immense user
 base at the moment, but it might in the future via mmdebstrap)

References: f495992428a396e0f98886c9a761a804aa161c68
Reported-By: Johannes Schauer Marin Rodrigues on IRC
Tested-By: Johannes Schauer Marin Rodrigues

1 files changed, 14 insertions, 11 deletions

diff --git a/apt-pkg/deb/debsystem.cc b/apt-pkg/deb/debsystem.cc
index a0200305d..c9c6a7e85 100644
--- a/apt-pkg/deb/debsystem.cc
+++ b/apt-pkg/deb/debsystem.cc
@@ -358,19 +358,22 @@ bool debSystem::FindIndex(pkgCache::PkgFileIterator File,
    return false;
 }
 									/*}}}*/
-
+std::string debSystem::StripDpkgChrootDirectory(std::string const &File)/*{{{*/
+{
+   // If the filename string begins with DPkg::Chroot-Directory, return the
+   // substr that is within the chroot so dpkg can access it.
+   std::string const chrootdir = _config->FindDir("DPkg::Chroot-Directory","/");
+   size_t len = chrootdir.length();
+   if (chrootdir == "/" || File.compare(0, len, chrootdir) != 0)
+      return File;
+   if (chrootdir.at(len - 1) == '/')
+      --len;
+   return File.substr(len);
+}
+									/*}}}*/
 std::string debSystem::GetDpkgExecutable()				/*{{{*/
 {
-   string Tmp = _config->Find("Dir::Bin::dpkg","dpkg");
-   string const dpkgChrootDir = _config->FindDir("DPkg::Chroot-Directory", "/");
-   size_t dpkgChrootLen = dpkgChrootDir.length();
-   if (dpkgChrootDir != "/" && Tmp.find(dpkgChrootDir) == 0)
-   {
-      if (dpkgChrootDir[dpkgChrootLen - 1] == '/')
-         --dpkgChrootLen;
-      Tmp = Tmp.substr(dpkgChrootLen);
-   }
-   return Tmp;
+   return StripDpkgChrootDirectory(_config->Find("Dir::Bin::dpkg","dpkg"));
 }
 									/*}}}*/
 std::vector<std::string> debSystem::GetDpkgBaseCommand()		/*{{{*/