【GTS-Fail】GtsSecurityHostTestCases#testNoExemptionsForSocketsBetweenCoreAndVendorBan

  • 2020 年 3 月 14 日
  • 筆記

【GTS-Fail】GtsSecurityHostTestCases#testNoExemptionsForSocketsBetweenCoreAndVendorBan

【問題描述】

Gts-7.0-r4工具報出失敗項
GtsSecurityHostTestCases
com.google.android.security.gts.SELinuxHostTest#testNoExemptionsForSocketsBetweenCoreAndVendorBan

    <Failure message="junit.framework.AssertionFailedError: Policy exempts domains from ban on socket communications between core and vendor: [hal_audio_default]">      <StackTrace>junit.framework.AssertionFailedError: Policy exempts domains from ban on socket communications between core and vendor: [hal_audio_default]      at junit.framework.Assert.fail(Assert.java:57)      at junit.framework.TestCase.fail(TestCase.java:227)      at com.google.android.security.gts.SELinuxHostTest.testNoExemptionsForSocketsBetweenCoreAndVendorBan(SELinuxHostTest.java:221)

這裡有個坑，報問題的時候說上個版本有，其實最終查證0004版本（2.20前）就有這個失敗項了，當時晶片廠商也告知是waiver項了。。。

【問題結論】

是waiver項
失敗項是由google的auto-patch程式碼導致，如果第一次遇到可以諮詢aml是否waiver。

AuthBlog：秋城https://www.cnblogs.com/houser0323

【分析詳細】

測試邏輯總覽
使用linux可執行程式：sepolicy-analyze，對機頂盒中的/sys/fs/selinux/policy文件進行解析，要求不能有返回值，命令是：
sepolicy-analyze policy attribute socket_between_core_and_vendor_violators
即：不允許有type（類型）與該attribute（屬性）「socket_between_core_and_vendor_violators」有關聯，字面意思：core與vendor的違規socket特權

system/sepolicy/tools/sepolicy-analyze/README

ATTRIBUTE (attribute)
sepolicy-analyze out/target/product//root/sepolicy attribute
Displays the types associated with the specified attribute name.

該許可權詳細限制在以下程式碼中有論述，Android TREBLE架構解耦計劃相關
system/sepolicy/prebuilts/api/26.0/public/domain.te
system/sepolicy/prebuilts/api/27.0/public/domain.te
system/sepolicy/prebuilts/api/28.0/public/domain.te:
system/sepolicy/public/domain.te

# On full TREBLE devices, socket communications between core components and vendor components are  # not permitted.  full_treble_only(`    # Most general rules first, more specific rules below.      # Core domains are not permitted to initiate communications to vendor domain sockets.    # We are not restricting the use of already established sockets because it is fine for a process    # to obtain an already established socket via some public/official/stable API and then exchange    # data with its peer over that socket. The wire format in this scenario is dicatated by the API    # and thus does not break the core-vendor separation.

梳理測試項邏輯
反編譯後定位測試項
./com/google/android/security/gts/SELinuxHostTest.java

    public void testNoExemptionsForVendorExecutingCore() throws Exception {          if (isFullTrebleDevice()) {              Set<String> types = sepolicyAnalyzeGetTypesAssociatedWithAttribute("vendor_executes_system_violators");//該語句是測試判斷，返回測試結果              if (!types.isEmpty()) {                  List<String> sortedTypes = new ArrayList(types);                  Collections.sort(sortedTypes);                  fail("Policy exempts vendor domains from ban on executing files in /system: " + sortedTypes);//此處assert，原因是容器types有東西，東西就是『[hal_audio_default]』              }          }      }

看一下方法的測試邏輯：sepolicyAnalyzeGetTypesAssociatedWithAttribute()
通過ProcessBuilder開啟一個進程，用於執行linux命令：sepolicy-analyze policy attribute socket_between_core_and_vendor_violators
然後獲取這個命令的標準輸出進行結果判斷

   private Set<String> sepolicyAnalyzeGetTypesAssociatedWithAttribute(String attribute) throws Exception {          BufferedReader in;          Throwable th;          Throwable th2;          Set<String> types = new HashSet();          //通過ProcessBuilder開啟一個進程，用於執行linux命令：sepolicy-analyze policy attribute socket_between_core_and_vendor_violators          ProcessBuilder pb = new ProcessBuilder(new String[]{this.mSepolicyAnalyze.getAbsolutePath(), this.mDevicePolicyFile.getAbsolutePath(), "attribute", attribute});  ......              in = new BufferedReader(new InputStreamReader(p.getInputStream()));              th = null;              while (true) {                  try {                      String type = in.readLine();                      if (type != null) {                          types.add(type.trim());//獲取有效標準輸出，寫到結果容器中存儲                      }}}  ......          return types;  ......      }

現在基本邏輯就清楚了，只要這個命令執行有結果返回就是不被允許的，現在需要分析這個工具『sepolicy-analyze』是幹嘛的？
在Android工程源碼中搜索，我們找到了這個host可執行程式的源碼
system/sepolicy/tools/sepolicy-analyze/
結合網路資料以及閱讀源碼和README文檔，澄清測試的命令用途：解析policy文件返回與attribute相關聯的type值

system/sepolicy/tools/sepolicy-analyze/README

63 ATTRIBUTE (attribute)
64 sepolicy-analyze out/target/product//root/sepolicy attribute
65
66 Displays the types associated with the specified attribute name.

工程中搜索確認
搜過確認一下到底在哪裡使得他們關聯的,定位到一下te文件

./system/sepolicy/vendor/hal_audio_default.te:1  type hal_audio_default, domain, socket_between_core_and_vendor_violators;

查證git log，我們發現是如下的commit導致的，是google的auto-path

commit 783f5b52195f0168f4c9db29b5a80ac63fb04020  Author: xxxxxx  Date:   Mon Feb 17 11:33:16 2020 +0800        auto patch added:CecAudio    diff --git a/vendor/hal_audio_default.te b/vendor/hal_audio_default.te  index 0dc2170..9da0f1b 100644  --- a/vendor/hal_audio_default.te  +++ b/vendor/hal_audio_default.te  @@ -1,4 +1,4 @@  -type hal_audio_default, domain;  +type hal_audio_default, domain, socket_between_core_and_vendor_violators; #此處添加的關聯，問題找到了根源   hal_server_domain(hal_audio_default, hal_audio)

到此，問題很大概率可確認為Google-waiver，因為引入問題的程式碼是Google的。接下來需向晶片廠商或Google溝通確認

由於報問題的烏龍，事實是該問題很久之前已澄清過，所以這一通分析並木有什麼卵用。。。。。。

VirMach 便宜 VPS

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