linker/linker_namespaces.cpp

/*
 * Copyright (C) 2016 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include "linker_namespaces.h"
#include "linker_globals.h"
#include "linker_soinfo.h"
#include "linker_utils.h"

#include <dlfcn.h>

// Given an absolute path, can this library be loaded into this namespace?
bool android_namespace_t::is_accessible(const std::string& file) {
  if (!is_isolated_) {
    return true;
  }

  if (!allowed_libs_.empty()) {
    const char *lib_name = basename(file.c_str());
    if (std::find(allowed_libs_.begin(), allowed_libs_.end(), lib_name) == allowed_libs_.end()) {
      return false;
    }
  }

  for (const auto& dir : ld_library_paths_) {
    if (file_is_in_dir(file, dir)) {
      return true;
    }
  }

  for (const auto& dir : default_library_paths_) {
    if (file_is_in_dir(file, dir)) {
      return true;
    }
  }

  for (const auto& dir : permitted_paths_) {
    if (file_is_under_dir(file, dir)) {
      return true;
    }
  }

  return false;
}

// Are symbols from this shared object accessible for symbol lookups in a library from this
// namespace?
bool android_namespace_t::is_accessible(soinfo* s) {
  auto is_accessible_ftor = [this] (soinfo* si, bool allow_secondary) {
    // This is workaround for apps hacking into soinfo list.
    // and inserting their own entries into it. (http://b/37191433)
    if (!si->has_min_version(3)) {
      DL_WARN("Warning: invalid soinfo version for \"%s\" (assuming inaccessible)",
              si->get_soname());
      return false;
    }

    if (si->get_primary_namespace() == this) {
      return true;
    }

    // When we're looking up symbols, we want to search libraries from the same namespace (whether
    // the namespace membership is primary or secondary), but we also want to search the immediate
    // dependencies of libraries in our namespace. (e.g. Supposing that libapp.so -> libandroid.so
    // crosses a namespace boundary, we want to search libandroid.so but not any of libandroid.so's
    // dependencies).
    //
    // Some libraries may be present in this namespace via the secondary namespace list:
    //  - the executable
    //  - LD_PRELOAD and DF_1_GLOBAL libraries
    //  - libraries inherited during dynamic namespace creation (e.g. because of
    //    RTLD_GLOBAL / DF_1_GLOBAL / ANDROID_NAMESPACE_TYPE_SHARED)
    //
    // When a library's membership is secondary, we want to search its symbols, but not the symbols
    // of its dependencies. The executable may depend on internal system libraries which should not
    // be searched.
    if (allow_secondary) {
      const android_namespace_list_t& secondary_namespaces = si->get_secondary_namespaces();
      if (secondary_namespaces.find(this) != secondary_namespaces.end()) {
        return true;
      }
    }

    return false;
  };

  if (is_accessible_ftor(s, true)) {
    return true;
  }

  return !s->get_parents().visit([&](soinfo* si) {
    return !is_accessible_ftor(si, false);
  });
}

// TODO: this is slightly unusual way to construct
// the global group for relocation. Not every RTLD_GLOBAL
// library is included in this group for backwards-compatibility
// reasons.
//
// This group consists of the main executable, LD_PRELOADs
// and libraries with the DF_1_GLOBAL flag set.
soinfo_list_t android_namespace_t::get_global_group() {
  soinfo_list_t global_group;
  soinfo_list().for_each([&](soinfo* si) {
    if ((si->get_dt_flags_1() & DF_1_GLOBAL) != 0) {
      global_group.push_back(si);
    }
  });

  return global_group;
}

// This function provides a list of libraries to be shared
// by the namespace. For the default namespace this is the global
// group (see get_global_group). For all others this is a group
// of RTLD_GLOBAL libraries (which includes the global group from
// the default namespace).
soinfo_list_t android_namespace_t::get_shared_group() {
  if (this == &g_default_namespace) {
    return get_global_group();
  }

  soinfo_list_t shared_group;
  soinfo_list().for_each([&](soinfo* si) {
    if ((si->get_rtld_flags() & RTLD_GLOBAL) != 0) {
      shared_group.push_back(si);
    }
  });

  return shared_group;
}