Handle the invalid timestamp in zipfile am: abf60c8d2e am: 69b259ccb4 am: 784cbd2c42

Change-Id: I9521cee9a8ed754af141be2d00e262a4732cc348

libziparchive/include/ziparchive/zip_archive.h

@@ -47,9 +47,10 @@ struct ZipEntry {
   // Modification time. The zipfile format specifies
   // that the first two little endian bytes contain the time
   // and the last two little endian bytes contain the date.
-  // See `GetModificationTime`.
+  // See `GetModificationTime`. Use signed integer to avoid the
+  // sub-overflow.
   // TODO: should be overridden by extra time field, if present.
-  uint32_t mod_time;
+  int32_t mod_time;
 
   // Returns `mod_time` as a broken-down struct tm.
   struct tm GetModificationTime() const;

libziparchive/zip_archive.cc

@@ -1299,6 +1299,7 @@ bool ZipArchive::InitializeCentralDirectory(off64_t cd_start_offset, size_t cd_s
   return true;
 }
 
+// This function returns the embedded timestamp as is; and doesn't perform validations.
 tm ZipEntry::GetModificationTime() const {
   tm t = {};