do not segfault in cache generation on mmap failure

Out of memory and similar circumstanzas could cause MMap::Map to fail
and especially the mmap/malloc calls in it. With some additional
checking we can avoid segfaults and similar in such situations – at
least in theory as if this is a real out of memory everything we do to
handle the error could just as well run into a memory problem as well…

But at least in theory (if MMap::Map is made to fail always) we can deal
with it so good that a user actually never sees a failure (as the cache
it tries to load with it fails and is discarded, so that DynamicMMap
takes over and a new one is build) instead of segfaulting.

Closes: 803417

1 files changed, 2 insertions, 0 deletions

diff --git a/apt-pkg/cachefile.cc b/apt-pkg/cachefile.cc
index aaa2436c5..39f1e72db 100644
--- a/apt-pkg/cachefile.cc
+++ b/apt-pkg/cachefile.cc
@@ -80,6 +80,8 @@ bool pkgCacheFile::BuildCaches(OpProgress *Progress, bool WithLock)
       if (file.IsOpen() == false || file.Failed())
 	 return false;
       Map = new MMap(file, MMap::Public|MMap::ReadOnly);
+      if (unlikely(Map->validData() == false))
+	 return false;
       Cache = new pkgCache(Map);
       return _error->PendingError() == false;
    }