securityd/src/SharedMemoryServer.cpp

   1 /*
   2  * Copyright (c) 2016-2017 Apple Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #include "SharedMemoryServer.h"
  25 #include <stdlib.h>
  26 #include <sys/mman.h>
  27 #include <sys/errno.h>
  28 #include <fcntl.h>
  29 #include <machine/byte_order.h>
  30 #include <string>
  31 #include <sys/stat.h>
  32 #include <security_utilities/crc.h>
  33 #include <security_utilities/casts.h>
  34 #include <unistd.h>
  35
  36 /*
  37     Logically, these should go in /var/run/mds, but we know that /var/db/mds
  38     already exists at install time.
  39 */
  40
  41 std::string SharedMemoryCommon::SharedMemoryFilePath(const char *segmentName, uid_t uid) {
  42     std::string path;
  43     uid = SharedMemoryCommon::fixUID(uid);
  44     path = SharedMemoryCommon::kMDSMessagesDirectory;   // i.e. /private/var/db/mds/messages/
  45     if (uid != 0) {
  46         path += std::to_string(uid) + "/";              // e.g. /private/var/db/mds/messages/501/
  47     }
  48
  49     path += SharedMemoryCommon::kUserPrefix;            // e.g. /var/db/mds/messages/se_
  50     path += segmentName;                                // e.g. /var/db/mds/messages/501/se_SecurityMessages
  51     return path;
  52 }
  53
  54 static bool makedir(const char *path, mode_t mode) {
  55     // Returns true on success. Primarily to centralize logging
  56     if (::mkdir(path, mode)==0 || errno==EEXIST) {
  57         return true;
  58     } else {
  59         secdebug("MDSPRIVACY","Failed to make directory: %s (%d)", path, errno);
  60         return false;
  61     }
  62 }
  63
  64 static void unlinkfile(const char *path) {
  65     // Primarily to centralize logging
  66     if (::unlink(path)==-1) {
  67          secdebug("MDSPRIVACY","Failed to unlink file: %s (%d)", path, errno);
  68     }
  69 }
  70
  71 SharedMemoryServer::SharedMemoryServer (const char* segmentName, SegmentOffsetType segmentSize, uid_t uid, gid_t gid) :
  72     mSegmentName (segmentName), mSegmentSize (segmentSize), mUID(SharedMemoryCommon::fixUID(uid))
  73 {
  74     const mode_t perm1777 = S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO;
  75     const mode_t perm0755 = S_IRWXU | (S_IRGRP | S_IXGRP) | (S_IROTH | S_IXOTH);
  76     const mode_t perm0600 = (S_IRUSR | S_IWUSR);
  77
  78     // make the mds directory, just in case it doesn't exist
  79     if (mUID == 0) {
  80         makedir(SharedMemoryCommon::kMDSDirectory, perm1777);
  81         makedir(SharedMemoryCommon::kMDSMessagesDirectory, perm0755);
  82     } else {
  83         // Assume kMDSMessagesDirectory was created first by securityd
  84         std::string uidstr = std::to_string(mUID);
  85         std::string upath = SharedMemoryCommon::kMDSMessagesDirectory;
  86         upath += "/" + uidstr;
  87         makedir(upath.c_str(), perm0755);
  88     }
  89     mFileName = SharedMemoryCommon::SharedMemoryFilePath(segmentName, uid);
  90
  91     // make the file name
  92     // clean any old file away
  93     unlinkfile(mFileName.c_str());
  94
  95     // open the file
  96     secdebug("MDSPRIVACY","creating %s",mFileName.c_str ());
  97     if(mUID != 0) {
  98         mBackingFile = open (mFileName.c_str (), O_RDWR | O_CREAT | O_EXCL, perm0600);
  99     }
 100     else {
 101         mBackingFile = open (mFileName.c_str (), O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
 102     }
 103
 104     if (mBackingFile < 0)
 105     {
 106         secdebug("MDSPRIVACY","creation of %s failed", mFileName.c_str());
 107         return;
 108     }
 109
 110     int rx = fchown(mBackingFile, uid, gid);
 111     if (rx) {
 112         secdebug("MDSPRIVACY","chown of %s to %d/%d failed : %d", mFileName.c_str(), uid, gid, rx);
 113     }
 114
 115     // set the segment size
 116     ftruncate (mBackingFile, segmentSize);
 117
 118     // map it into memory
 119     mSegment = (u_int8_t*) mmap (NULL, mSegmentSize, PROT_READ | PROT_WRITE, MAP_SHARED, mBackingFile, 0);
 120
 121     if (mSegment == MAP_FAILED) // can't map the memory?
 122     {
 123         mSegment = NULL;
 124         unlinkfile(mFileName.c_str());
 125     } else {
 126         mDataPtr = mDataArea = mSegment + sizeof(SegmentOffsetType);
 127         mDataMax = mSegment + segmentSize;;
 128
 129         SetProducerOffset (0);
 130     }
 131 }
 132
 133 SharedMemoryServer::~SharedMemoryServer ()
 134 {
 135         // go away
 136         if (mSegment == NULL)
 137         {
 138                 return;
 139         }
 140
 141         // get out of memory
 142         munmap (mSegment, mSegmentSize);
 143
 144     close(mBackingFile);
 145
 146         // mark the segment for deletion
 147         unlinkfile(mFileName.c_str ());
 148 }
 149
 150
 151
 152 const SegmentOffsetType
 153         kSegmentLength = 0,
 154         kCRCOffset = kSegmentLength + sizeof(SegmentOffsetType),
 155         kDomainOffset = kCRCOffset + sizeof(SegmentOffsetType),
 156         kEventTypeOffset = kDomainOffset + sizeof(SegmentOffsetType),
 157         kHeaderLength = kEventTypeOffset + sizeof(SegmentOffsetType) - kCRCOffset;
 158
 159 void SharedMemoryServer::WriteMessage (SegmentOffsetType domain, SegmentOffsetType event, const void *message, SegmentOffsetType messageLength)
 160 {
 161     // backing file MUST be right size, don't ftruncate() more then needed though to avoid reaching too deep into filesystem
 162     struct stat sb;
 163     if (::fstat(mBackingFile, &sb) == 0 && sb.st_size != (off_t)mSegmentSize) {
 164         ::ftruncate(mBackingFile, mSegmentSize);
 165     }
 166
 167         // assemble the final message
 168         ssize_t messageSize = kHeaderLength + messageLength;
 169         u_int8_t finalMessage[messageSize];
 170         SegmentOffsetType *fm  = (SegmentOffsetType*) finalMessage;
 171         fm[0] = OSSwapHostToBigInt32(domain);
 172         fm[1] = OSSwapHostToBigInt32(event);
 173         memcpy(&fm[2], message, messageLength);
 174
 175         SegmentOffsetType crc = CalculateCRC(finalMessage, messageSize);
 176
 177         // write the length
 178         WriteOffset(int_cast<size_t, SegmentOffsetType>(messageSize));
 179
 180         // write the crc
 181         WriteOffset(crc);
 182
 183         // write the data
 184         WriteData (finalMessage, int_cast<size_t, SegmentOffsetType>(messageSize));
 185
 186         // write the data count
 187         SetProducerOffset(int_cast<size_t, SegmentOffsetType>(mDataPtr - mDataArea));
 188 }
 189
 190
 191
 192 const char* SharedMemoryServer::GetSegmentName ()
 193 {
 194         return mSegmentName.c_str ();
 195 }
 196
 197
 198
 199 size_t SharedMemoryServer::GetSegmentSize ()
 200 {
 201         return mSegmentSize;
 202 }
 203
 204
 205 void SharedMemoryServer::SetProducerOffset (SegmentOffsetType producerCount)
 206 {
 207         *((SegmentOffsetType*) mSegment) = OSSwapHostToBigInt32 (producerCount);
 208 }
 209
 210
 211
 212 void SharedMemoryServer::WriteOffset(SegmentOffsetType offset)
 213 {
 214         u_int8_t buffer[4];
 215         *((u_int32_t*) buffer) = OSSwapHostToBigInt32(offset);
 216         WriteData(buffer, 4);
 217 }
 218
 219
 220
 221 void SharedMemoryServer::WriteData(const void* data, SegmentOffsetType length)
 222 {
 223         // figure out where in the buffer we actually need to write the data
 224         // figure out how many bytes we can write without overflowing the buffer
 225         const u_int8_t* dp = (const u_int8_t*) data;
 226         SegmentOffsetType bytesToEnd = int_cast<ptrdiff_t, SegmentOffsetType>(mDataMax - mDataPtr);
 227
 228         // figure out how many bytes we can write
 229         SegmentOffsetType bytesToWrite = (length <= bytesToEnd) ? length : bytesToEnd;
 230
 231         // move the first part of the data, making sure to skip the producer pointer
 232         memcpy (mDataPtr, dp, bytesToWrite);
 233         mDataPtr += bytesToWrite;
 234         dp += bytesToWrite;
 235
 236         // deduct the bytes just written
 237         length -= bytesToWrite;
 238
 239         if (length != 0) // did we wrap around?
 240         {
 241                 mDataPtr = mDataArea;
 242                 memcpy (mDataPtr, dp, length);
 243                 mDataPtr += length;
 244         }
 245 }