Forbid extracting files with absolute path from 'cpio' archives (boo#1122683)

Also fix and modernize the code, add tests.

tests/fixtures/README

@@ -26,3 +26,10 @@ Create archive.ar
 ar qP archive.ar /tmp/foo /123 very-long-long-long-long-name very-long-long-long-long-name2 'very-long-name
 -with-newline' 'a
 b' dir/file
+
+
+Create archive.cpio
+-------------------
+
+printf "/tmp/foo\0/123\0very-long-long-long-long-name\0very-long-long-long-long-name2\0very-long-name
+-with-newline\0a\nb\0dir/file\0" | cpio -ocv0 --owner=root:root > archive.cpio

tests/test_util_cpio.py

@@ -0,0 +1,71 @@
+import os
+import shutil
+import tempfile
+import unittest
+
+from osc.util.cpio import CpioRead
+from osc.util.cpio import CpioError
+
+
+FIXTURES_DIR = os.path.join(os.path.dirname(__file__), "fixtures")
+
+
+class TestCpio(unittest.TestCase):
+    def setUp(self):
+        self.tmpdir = tempfile.mkdtemp(prefix="osc_test_")
+        try:
+            self.old_cwd = os.getcwd()
+        except FileNotFoundError:
+            self.old_cwd = os.path.expanduser("~")
+        os.chdir(self.tmpdir)
+        self.archive = os.path.join(FIXTURES_DIR, "archive.cpio")
+        self.cpio = CpioRead(self.archive)
+        self.cpio.read()
+
+    def tearDown(self):
+        os.chdir(self.old_cwd)
+        shutil.rmtree(self.tmpdir)
+
+    def test_file_list(self):
+        actual = [i.filename for i in self.cpio]
+        expected = [
+            # absolute path
+            b"/tmp/foo",
+            # this is a filename, not a long filename reference
+            b"/123",
+            b"very-long-long-long-long-name",
+            b"very-long-long-long-long-name2",
+            # long file name with a newline
+            b"very-long-name\n-with-newline",
+            # short file name with a newline
+            b"a\nb",
+            b"dir/file",
+        ]
+        self.assertEqual(actual, expected)
+
+    def test_copyin_file(self):
+        path = self.cpio.copyin_file("a\nb", dest=self.tmpdir)
+
+        # check that we've got the expected path
+        self.assertEqual(path, os.path.join(self.tmpdir, "a\nb"))
+
+        # ... and that the contents also match
+        with open(path, "r", encoding="utf-8") as f:
+            self.assertEqual(f.read(), "newline\n")
+
+    def test_copyin_file_abspath(self):
+        self.assertRaises(CpioError, self.cpio.copyin_file, "/tmp/foo")
+
+    def test_copyin_file_subdir(self):
+        path = self.cpio.copyin_file("dir/file", dest=self.tmpdir)
+
+        # check that we've got the expected path
+        self.assertEqual(path, os.path.join(self.tmpdir, "dir/file"))
+
+        # ... and that the contents also match
+        with open(path, "r", encoding="utf-8") as f:
+            self.assertEqual(f.read(), "file-in-a-dir\n")
+
+
+if __name__ == "__main__":
+    unittest.main()