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Commit 54543793 authored by Eric Biggers's avatar Eric Biggers
Browse files

Zygote: relabel to either system_userdir_file or system_data_file 

To hide other apps' data directories, zygote mounts tmpfs instances over
various directories such as /data/user, then bind-mounts in the needed
app directories.  Files in tmpfs get the SELinux label "tmpfs" by
default.  After creating them, zygote relabels some of these "tmpfs"
files to their normal labels; however, in every case the desired label
was "u:object_r:system_data_file:s0", so zygote just copied the label of
/data/user_de which happened to have this same label.

With https://r.android.com/2078213, the /data/user_de directory, but not
its subdirectories, will start being labeled as
"u:object_r:system_userdir_file:s0".  This would break the
above-mentioned logic, as it would start assigning system_userdir_file
to files that should be system_data_file.  Therefore, update it to
assign the appropriate type of [system_userdir_file, system_data_file].

Note that alternatively, it seems that we could just always use
system_data_file, or just remove this relabeling code entirely since the
sepolicy contains 'allow domain tmpfs:dir search' anyway.  But as long
as zygote is trying to set the normal labels, it should do it correctly.

Test: Tested together with the sepolicy change
      https://r.android.com/2078213; see there for testing notes.
Bug: 156305599
Change-Id: I325aa873cf216e33924d0508100fcc755f265cf2
parent 3d9c19f2

core/jni/com_android_internal_os_Zygote.cpp

+25 −16
Original line number Diff line number Diff line
@@ -1153,8 +1153,8 @@ static void relabelDir(const char* path, const char* context, fail_fn_t fail_fn) 
  }

}



// Relabel all directories under a path non-recursively.

static void relabelAllDirs(const char* path, const char* context, fail_fn_t fail_fn) {

// Relabel the subdirectories and symlinks in the given directory, non-recursively.

static void relabelSubdirs(const char* path, const char* context, fail_fn_t fail_fn) {

  DIR* dir = opendir(path);

  if (dir == nullptr) {

    fail_fn(CREATE_ERROR("Failed to opendir %s", path));
@@ -1231,11 +1231,19 @@ static void isolateAppData(JNIEnv* env, const std::vector<std::string>& merged_d 
  snprintf(internalDePath, PATH_MAX, "/data/user_de");

  snprintf(externalPrivateMountPath, PATH_MAX, "/mnt/expand");



  char* dataDataContext = nullptr;

  if (getfilecon(internalDePath, &dataDataContext) < 0) {

    fail_fn(CREATE_ERROR("Unable to getfilecon on %s %s", internalDePath,

  // Get the "u:object_r:system_userdir_file:s0" security context.  This can be

  // gotten from several different places; we use /data/user.

  char* dataUserdirContext = nullptr;

  if (getfilecon(internalCePath, &dataUserdirContext) < 0) {

    fail_fn(CREATE_ERROR("Unable to getfilecon on %s %s", internalCePath,

        strerror(errno)));

  }

  // Get the "u:object_r:system_data_file:s0" security context.  This can be

  // gotten from several different places; we use /data/misc.

  char* dataFileContext = nullptr;

  if (getfilecon("/data/misc", &dataFileContext) < 0) {

    fail_fn(CREATE_ERROR("Unable to getfilecon on /data/misc %s", strerror(errno)));

  }



  MountAppDataTmpFs(internalLegacyCePath, fail_fn);

  MountAppDataTmpFs(internalCePath, fail_fn);
@@ -1330,19 +1338,19 @@ static void isolateAppData(JNIEnv* env, const std::vector<std::string>& merged_d 
  // the file operations on tmpfs. If we set the label when we mount

  // tmpfs, SELinux will not happy as we are changing system_data_files.

  // Relabel dir under /data/user, including /data/user/0

  relabelAllDirs(internalCePath, dataDataContext, fail_fn);

  relabelSubdirs(internalCePath, dataFileContext, fail_fn);



  // Relabel /data/user

  relabelDir(internalCePath, dataDataContext, fail_fn);

  relabelDir(internalCePath, dataUserdirContext, fail_fn);



  // Relabel /data/data

  relabelDir(internalLegacyCePath, dataDataContext, fail_fn);

  relabelDir(internalLegacyCePath, dataFileContext, fail_fn);



  // Relabel dir under /data/user_de

  relabelAllDirs(internalDePath, dataDataContext, fail_fn);

  // Relabel subdirectories of /data/user_de

  relabelSubdirs(internalDePath, dataFileContext, fail_fn);



  // Relabel /data/user_de

  relabelDir(internalDePath, dataDataContext, fail_fn);

  relabelDir(internalDePath, dataUserdirContext, fail_fn);



  // Relabel CE and DE dirs under /mnt/expand

  dir = opendir(externalPrivateMountPath);
@@ -1355,14 +1363,15 @@ static void isolateAppData(JNIEnv* env, const std::vector<std::string>& merged_d 
    auto cePath = StringPrintf("%s/user", volPath.c_str());

    auto dePath = StringPrintf("%s/user_de", volPath.c_str());



    relabelAllDirs(cePath.c_str(), dataDataContext, fail_fn);

    relabelDir(cePath.c_str(), dataDataContext, fail_fn);

    relabelAllDirs(dePath.c_str(), dataDataContext, fail_fn);

    relabelDir(dePath.c_str(), dataDataContext, fail_fn);

    relabelSubdirs(cePath.c_str(), dataFileContext, fail_fn);

    relabelDir(cePath.c_str(), dataUserdirContext, fail_fn);

    relabelSubdirs(dePath.c_str(), dataFileContext, fail_fn);

    relabelDir(dePath.c_str(), dataUserdirContext, fail_fn);

  }

  closedir(dir);



  freecon(dataDataContext);

  freecon(dataUserdirContext);

  freecon(dataFileContext);

}



static void insertPackagesToMergedList(JNIEnv* env,