fail instead of segfault on unreadable config files

The report mentions "apt list --upgradable", but there are others which
have inconsistent behavior ranging from segfaulting to doing something
with the partial (and hence incomplete) data. We had a recent report
about sources.list (#818628), this one mentions prefences, the obvious
next step is conf files… so the testcase is adapted to check for all
three in file and directory versions and run a bunch of commands each
time which should all have more or less the same behavior in such a case
(aka error out).

Closes: 824503
(cherry picked from commit fdf9eef4d96a18d0167708499c993e1174251e88)

1 files changed, 9 insertions, 4 deletions

diff --git a/apt-private/private-cacheset.cc b/apt-private/private-cacheset.cc
index 981766cdf..52cd22d2a 100644
--- a/apt-private/private-cacheset.cc
+++ b/apt-private/private-cacheset.cc
@@ -30,13 +30,18 @@ bool GetLocalitySortedVersionSet(pkgCacheFile &CacheFile,
                                  Matcher &matcher,
                                  OpProgress * const progress)
 {
-   pkgCache *Cache = CacheFile.GetPkgCache();
-   pkgDepCache *DepCache = CacheFile.GetDepCache();
+   pkgCache * const Cache = CacheFile.GetPkgCache();
+   if (unlikely(Cache == nullptr))
+      return false;
+   if (progress != nullptr)
+      progress->SubProgress(Cache->Head().PackageCount, _("Sorting"));
+
+   pkgDepCache * const DepCache = CacheFile.GetDepCache();
+   if (unlikely(DepCache == nullptr))
+      return false;
    APT::CacheSetHelper helper(false);
 
    int Done=0;
-   if (progress != NULL)
-      progress->SubProgress(Cache->Head().PackageCount, _("Sorting"));
 
    bool const insertCurrentVer = _config->FindB("APT::Cmd::Installed", false);
    bool const insertUpgradable = _config->FindB("APT::Cmd::Upgradable", false);