1 /* 2 * Copyright (C) 2018 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include "idmap2/FileUtils.h" 18 19 #include <random> 20 #include <string> 21 #include <string_view> 22 23 #include "android-base/file.h" 24 #include "android-base/macros.h" 25 #include "android-base/strings.h" 26 #include "private/android_filesystem_config.h" 27 28 namespace android::idmap2::utils { 29 30 #ifdef __ANDROID__ UidHasWriteAccessToPath(uid_t uid,const std::string & path)31 bool UidHasWriteAccessToPath(uid_t uid, const std::string& path) { 32 // resolve symlinks and relative paths; the directories must exist 33 std::string canonical_path; 34 if (!base::Realpath(base::Dirname(path), &canonical_path)) { 35 return false; 36 } 37 38 if (base::StartsWith(canonical_path, kIdmapCacheDir) && 39 (canonical_path.size() == kIdmapCacheDir.size() || 40 canonical_path[kIdmapCacheDir.size()] == '/')) { 41 // limit access to /data/resource-cache to root and system 42 return uid == AID_ROOT || uid == AID_SYSTEM; 43 } 44 return true; 45 } 46 #else 47 bool UidHasWriteAccessToPath(uid_t uid ATTRIBUTE_UNUSED, const std::string& path ATTRIBUTE_UNUSED) { 48 return true; 49 } 50 #endif 51 RandomStringForPath(size_t length)52 std::string RandomStringForPath(size_t length) { 53 constexpr std::string_view kChars = 54 "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; 55 56 std::string out_rand; 57 out_rand.resize(length); 58 59 static thread_local std::random_device rd; 60 std::uniform_int_distribution<int> dist(0, kChars.size() - 1); 61 for (size_t i = 0; i < length; i++) { 62 out_rand[i] = kChars[dist(rd)]; 63 } 64 return out_rand; 65 } 66 67 } // namespace android::idmap2::utils 68