flat_hash: use mkstemp in _setitem

Fix the _setitem method to use mkstemp in order to avoid a
race condition when multiple pid namespaces share the same
cache directory.

Reported-by: Mike Frysinger <vapier@chromium.org>
X-Chromium-Bug: 477727
X-Chromium-Bug-url: https://bugs.chromium.org/p/chromium/issues/detail?id=477727

pym/portage/cache/flat_hash.py

@@ -1,4 +1,4 @@
-# Copyright 2005-2014 Gentoo Foundation
+# Copyright 2005-2016 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 # Author(s): Brian Harring (ferringb@gentoo.org)
 
@@ -10,6 +10,7 @@
 import io
 import stat
 import sys
+import tempfile
 import os as _os
 from portage import os
 from portage import _encodings
@@ -66,27 +67,14 @@ def _parse_data(self, data, cpv):
 			raise cache_errors.CacheCorruption(cpv, e)
 
 	def _setitem(self, cpv, values):
-		s = cpv.rfind("/")
-		fp = os.path.join(self.location,cpv[:s],".update.%i.%s" % (os.getpid(), cpv[s+1:]))
 		try:
-			myf = io.open(_unicode_encode(fp,
-				encoding=_encodings['fs'], errors='strict'),
-				mode='w', encoding=_encodings['repo.content'],
-				errors='backslashreplace')
-		except (IOError, OSError) as e:
-			if errno.ENOENT == e.errno:
-				try:
-					self._ensure_dirs(cpv)
-					myf = io.open(_unicode_encode(fp,
-						encoding=_encodings['fs'], errors='strict'),
-						mode='w', encoding=_encodings['repo.content'],
-						errors='backslashreplace')
-				except (OSError, IOError) as e:
-					raise cache_errors.CacheCorruption(cpv, e)
-			else:
-				raise cache_errors.CacheCorruption(cpv, e)
+			fd, fp = tempfile.mkstemp(dir=self.location)
+		except EnvironmentError as e:
+			raise cache_errors.CacheCorruption(cpv, e)
 
-		try:
+		with io.open(fd, mode='w',
+			encoding=_encodings['repo.content'],
+			errors='backslashreplace') as myf:
 			for k in self._write_keys:
 				v = values.get(k)
 				if not v:
@@ -95,18 +83,29 @@ def _setitem(self, cpv, values):
 				# k and v are coerced to unicode, in order to prevent TypeError
 				# when writing raw bytes to TextIOWrapper with Python 2.
 				myf.write("%s=%s\n" % (k, v))
-		finally:
-			myf.close()
+
 		self._ensure_access(fp)
 
 		#update written.  now we move it.
 
 		new_fp = os.path.join(self.location,cpv)
 		try:
 			os.rename(fp, new_fp)
-		except (OSError, IOError) as e:
-			os.remove(fp)
-			raise cache_errors.CacheCorruption(cpv, e)
+		except EnvironmentError as e:
+			success = False
+			try:
+				if errno.ENOENT == e.errno:
+					try:
+						self._ensure_dirs(cpv)
+						os.rename(fp, new_fp)
+						success = True
+					except EnvironmentError as e:
+						raise cache_errors.CacheCorruption(cpv, e)
+				else:
+					raise cache_errors.CacheCorruption(cpv, e)
+			finally:
+				if not success:
+					os.remove(fp)
 
 	def _delitem(self, cpv):
 #		import pdb;pdb.set_trace()