1 /* 2 ** Copyright 2017, 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 "FileBlobCache.h" 18 19 #include <errno.h> 20 #include <inttypes.h> 21 #include <log/log.h> 22 #include <sys/mman.h> 23 #include <sys/stat.h> 24 25 26 // Cache file header 27 static const char* cacheFileMagic = "EGL$"; 28 static const size_t cacheFileHeaderSize = 8; 29 30 namespace android { 31 32 static uint32_t crc32c(const uint8_t* buf, size_t len) { 33 const uint32_t polyBits = 0x82F63B78; 34 uint32_t r = 0; 35 for (size_t i = 0; i < len; i++) { 36 r ^= buf[i]; 37 for (int j = 0; j < 8; j++) { 38 if (r & 1) { 39 r = (r >> 1) ^ polyBits; 40 } else { 41 r >>= 1; 42 } 43 } 44 } 45 return r; 46 } 47 48 FileBlobCache::FileBlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize, 49 const std::string& filename) 50 : BlobCache(maxKeySize, maxValueSize, maxTotalSize) 51 , mFilename(filename) { 52 if (mFilename.length() > 0) { 53 size_t headerSize = cacheFileHeaderSize; 54 55 int fd = open(mFilename.c_str(), O_RDONLY, 0); 56 if (fd == -1) { 57 if (errno != ENOENT) { 58 ALOGE("error opening cache file %s: %s (%d)", mFilename.c_str(), 59 strerror(errno), errno); 60 } 61 return; 62 } 63 64 struct stat statBuf; 65 if (fstat(fd, &statBuf) == -1) { 66 ALOGE("error stat'ing cache file: %s (%d)", strerror(errno), errno); 67 close(fd); 68 return; 69 } 70 71 // Sanity check the size before trying to mmap it. 72 size_t fileSize = statBuf.st_size; 73 if (fileSize > mMaxTotalSize * 2) { 74 ALOGE("cache file is too large: %#" PRIx64, 75 static_cast<off64_t>(statBuf.st_size)); 76 close(fd); 77 return; 78 } 79 80 uint8_t* buf = reinterpret_cast<uint8_t*>(mmap(nullptr, fileSize, 81 PROT_READ, MAP_PRIVATE, fd, 0)); 82 if (buf == MAP_FAILED) { 83 ALOGE("error mmaping cache file: %s (%d)", strerror(errno), 84 errno); 85 close(fd); 86 return; 87 } 88 89 // Check the file magic and CRC 90 size_t cacheSize = fileSize - headerSize; 91 if (memcmp(buf, cacheFileMagic, 4) != 0) { 92 ALOGE("cache file has bad mojo"); 93 close(fd); 94 return; 95 } 96 uint32_t* crc = reinterpret_cast<uint32_t*>(buf + 4); 97 if (crc32c(buf + headerSize, cacheSize) != *crc) { 98 ALOGE("cache file failed CRC check"); 99 close(fd); 100 return; 101 } 102 103 int err = unflatten(buf + headerSize, cacheSize); 104 if (err < 0) { 105 ALOGE("error reading cache contents: %s (%d)", strerror(-err), 106 -err); 107 munmap(buf, fileSize); 108 close(fd); 109 return; 110 } 111 112 munmap(buf, fileSize); 113 close(fd); 114 } 115 } 116 117 void FileBlobCache::writeToFile() { 118 if (mFilename.length() > 0) { 119 size_t cacheSize = getFlattenedSize(); 120 size_t headerSize = cacheFileHeaderSize; 121 const char* fname = mFilename.c_str(); 122 123 // Try to create the file with no permissions so we can write it 124 // without anyone trying to read it. 125 int fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0); 126 if (fd == -1) { 127 if (errno == EEXIST) { 128 // The file exists, delete it and try again. 129 if (unlink(fname) == -1) { 130 // No point in retrying if the unlink failed. 131 ALOGE("error unlinking cache file %s: %s (%d)", fname, 132 strerror(errno), errno); 133 return; 134 } 135 // Retry now that we've unlinked the file. 136 fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0); 137 } 138 if (fd == -1) { 139 ALOGE("error creating cache file %s: %s (%d)", fname, 140 strerror(errno), errno); 141 return; 142 } 143 } 144 145 size_t fileSize = headerSize + cacheSize; 146 147 uint8_t* buf = new uint8_t [fileSize]; 148 if (!buf) { 149 ALOGE("error allocating buffer for cache contents: %s (%d)", 150 strerror(errno), errno); 151 close(fd); 152 unlink(fname); 153 return; 154 } 155 156 int err = flatten(buf + headerSize, cacheSize); 157 if (err < 0) { 158 ALOGE("error writing cache contents: %s (%d)", strerror(-err), 159 -err); 160 delete [] buf; 161 close(fd); 162 unlink(fname); 163 return; 164 } 165 166 // Write the file magic and CRC 167 memcpy(buf, cacheFileMagic, 4); 168 uint32_t* crc = reinterpret_cast<uint32_t*>(buf + 4); 169 *crc = crc32c(buf + headerSize, cacheSize); 170 171 if (write(fd, buf, fileSize) == -1) { 172 ALOGE("error writing cache file: %s (%d)", strerror(errno), 173 errno); 174 delete [] buf; 175 close(fd); 176 unlink(fname); 177 return; 178 } 179 180 delete [] buf; 181 fchmod(fd, S_IRUSR); 182 close(fd); 183 } 184 } 185 186 } 187
