commit 1da49dc9b4f5605990f600e15f6f3c584fe2c0dc
author Mårten Kongstad <marten.kongstad@sony.com> Mon Jan 14 10:03:53 2019 +0100
committer Todd Kennedy <toddke@google.com> Fri Jan 18 10:05:48 2019 -0800
tree 4b2257c309d93e4aafbf07a4a13a0b9347b7d760
parent 793f1a793c2b9cd8f7356b83b8a2e5fd8d444e9b

idmap2: lock down write access to /data/resouce-cache

Deny write access to /data/resource-cache for UIDs other than root and
system. While this is already handled by SELinux rules, add an
additional layer of security to explicitly prevent malicious apps from
messing with the system's idmap files.

Test: make idmap2_tests
Change-Id: Id986633558d5d02452276f05f64337a8700f148a

cmds/idmap2/tests/FileUtilsTests.cpp

diff --git a/cmds/idmap2/tests/FileUtilsTests.cpp b/cmds/idmap2/tests/FileUtilsTests.cpp
index d9d9a7f..45f84fe 100644
--- a/cmds/idmap2/tests/FileUtilsTests.cpp
+++ b/cmds/idmap2/tests/FileUtilsTests.cpp
@@ -22,6 +22,8 @@
 #include "gtest/gtest.h"
 
 #include "android-base/macros.h"
+#include "android-base/stringprintf.h"
+#include "private/android_filesystem_config.h"
 
 #include "idmap2/FileUtils.h"
 
@@ -71,4 +73,25 @@
   close(pipefd[0]);
 }
 
+#ifdef __ANDROID__
+TEST(FileUtilsTests, UidHasWriteAccessToPath) {
+  constexpr const char* tmp_path = "/data/local/tmp/test@idmap";
+  const std::string cache_path(base::StringPrintf("%s/test@idmap", kIdmapCacheDir));
+  const std::string sneaky_cache_path(base::StringPrintf("/data/../%s/test@idmap", kIdmapCacheDir));
+
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_ROOT, tmp_path));
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_ROOT, cache_path));
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_ROOT, sneaky_cache_path));
+
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_SYSTEM, tmp_path));
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_SYSTEM, cache_path));
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_SYSTEM, sneaky_cache_path));
+
+  constexpr const uid_t AID_SOME_APP = AID_SYSTEM + 1;
+  ASSERT_TRUE(UidHasWriteAccessToPath(AID_SOME_APP, tmp_path));
+  ASSERT_FALSE(UidHasWriteAccessToPath(AID_SOME_APP, cache_path));
+  ASSERT_FALSE(UidHasWriteAccessToPath(AID_SOME_APP, sneaky_cache_path));
+}
+#endif
+
 }  // namespace android::idmap2::utils