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 static bool makedir(const char *path, mode_t mode) {
  42     // Returns true on success. Primarily to centralize logging
  43     if (::mkdir(path, mode)==0 || errno==EEXIST) {
  44         return true;
  45     } else {
  46         secdebug("MDSPRIVACY","Failed to make directory: %s (%d)", path, errno);
  47         return false;
  48     }
  49 }
  50
  51 static void unlinkfile(const char *path) {
  52     // Primarily to centralize logging
  53     if (::unlink(path)==-1) {
  54          secdebug("MDSPRIVACY","Failed to unlink file: %s (%d)", path, errno);
  55     }
  56 }
  57
  58 SharedMemoryServer::SharedMemoryServer (const char* segmentName, SegmentOffsetType segmentSize, uid_t uid, gid_t gid) :
  59     mSegmentName (segmentName), mSegmentSize (segmentSize), mUID(SharedMemoryCommon::fixUID(uid))
  60 {
  61     const mode_t perm1777 = S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO;
  62     const mode_t perm0755 = S_IRWXU | (S_IRGRP | S_IXGRP) | (S_IROTH | S_IXOTH);
  63     const mode_t perm0600 = (S_IRUSR | S_IWUSR);
  64
  65     // make the mds directory, just in case it doesn't exist
  66     if (mUID == 0) {
  67         makedir(SharedMemoryCommon::kMDSDirectory, perm1777);
  68         makedir(SharedMemoryCommon::kMDSMessagesDirectory, perm0755);
  69     } else {
  70         // Assume kMDSMessagesDirectory was created first by securityd
  71         std::string uidstr = std::to_string(mUID);
  72         std::string upath = SharedMemoryCommon::kMDSMessagesDirectory;
  73         upath += "/" + uidstr;
  74         makedir(upath.c_str(), perm0755);
  75     }
  76     mFileName = SharedMemoryCommon::SharedMemoryFilePath(segmentName, uid);
  77
  78     // make the file name
  79     // clean any old file away
  80     unlinkfile(mFileName.c_str());
  81
  82     // open the file
  83     secdebug("MDSPRIVACY","creating %s",mFileName.c_str ());
  84     if(mUID != 0) {
  85         mBackingFile = open (mFileName.c_str (), O_RDWR | O_CREAT | O_EXCL, perm0600);
  86     }
  87     else {
  88         mBackingFile = open (mFileName.c_str (), O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
  89     }
  90
  91     if (mBackingFile < 0)
  92     {
  93         secdebug("MDSPRIVACY","creation of %s failed", mFileName.c_str());
  94         return;
  95     }
  96
  97     int rx = fchown(mBackingFile, uid, gid);
  98     if (rx) {
  99         secdebug("MDSPRIVACY","chown of %s to %d/%d failed : %d", mFileName.c_str(), uid, gid, rx);
 100     }
 101
 102     // set the segment size
 103     ftruncate (mBackingFile, segmentSize);
 104
 105     // map it into memory
 106     mSegment = (u_int8_t*) mmap (NULL, mSegmentSize, PROT_READ | PROT_WRITE, MAP_SHARED, mBackingFile, 0);
 107
 108     if (mSegment == MAP_FAILED) // can't map the memory?
 109     {
 110         mSegment = NULL;
 111         unlinkfile(mFileName.c_str());
 112     } else {
 113         mDataPtr = mDataArea = mSegment + sizeof(SegmentOffsetType);
 114         mDataMax = mSegment + segmentSize;;
 115
 116         SetProducerOffset (0);
 117     }
 118 }
 119
 120 SharedMemoryServer::~SharedMemoryServer ()
 121 {
 122         // go away
 123         if (mSegment == NULL)
 124         {
 125                 return;
 126         }
 127
 128         // get out of memory
 129         munmap (mSegment, mSegmentSize);
 130
 131     close(mBackingFile);
 132
 133         // mark the segment for deletion
 134         unlinkfile(mFileName.c_str ());
 135 }
 136
 137
 138
 139 const SegmentOffsetType
 140         kSegmentLength = 0,
 141         kCRCOffset = kSegmentLength + sizeof(SegmentOffsetType),
 142         kDomainOffset = kCRCOffset + sizeof(SegmentOffsetType),
 143         kEventTypeOffset = kDomainOffset + sizeof(SegmentOffsetType),
 144         kHeaderLength = kEventTypeOffset + sizeof(SegmentOffsetType) - kCRCOffset;
 145
 146 void SharedMemoryServer::WriteMessage (SegmentOffsetType domain, SegmentOffsetType event, const void *message, SegmentOffsetType messageLength)
 147 {
 148     // backing file MUST be right size, don't ftruncate() more then needed though to avoid reaching too deep into filesystem
 149     struct stat sb;
 150     if (::fstat(mBackingFile, &sb) == 0 && sb.st_size != (off_t)mSegmentSize) {
 151         ::ftruncate(mBackingFile, mSegmentSize);
 152     }
 153
 154         // assemble the final message
 155         ssize_t messageSize = kHeaderLength + messageLength;
 156         u_int8_t finalMessage[messageSize];
 157         SegmentOffsetType *fm  = (SegmentOffsetType*) finalMessage;
 158         fm[0] = OSSwapHostToBigInt32(domain);
 159         fm[1] = OSSwapHostToBigInt32(event);
 160         memcpy(&fm[2], message, messageLength);
 161
 162         SegmentOffsetType crc = CalculateCRC(finalMessage, messageSize);
 163
 164         // write the length
 165         WriteOffset(int_cast<size_t, SegmentOffsetType>(messageSize));
 166
 167         // write the crc
 168         WriteOffset(crc);
 169
 170         // write the data
 171         WriteData (finalMessage, int_cast<size_t, SegmentOffsetType>(messageSize));
 172
 173         // write the data count
 174         SetProducerOffset(int_cast<size_t, SegmentOffsetType>(mDataPtr - mDataArea));
 175 }
 176
 177
 178
 179 const char* SharedMemoryServer::GetSegmentName ()
 180 {
 181         return mSegmentName.c_str ();
 182 }
 183
 184
 185
 186 size_t SharedMemoryServer::GetSegmentSize ()
 187 {
 188         return mSegmentSize;
 189 }
 190
 191
 192 void SharedMemoryServer::SetProducerOffset (SegmentOffsetType producerCount)
 193 {
 194         *((SegmentOffsetType*) mSegment) = OSSwapHostToBigInt32 (producerCount);
 195 }
 196
 197
 198
 199 void SharedMemoryServer::WriteOffset(SegmentOffsetType offset)
 200 {
 201         u_int8_t buffer[4];
 202         *((u_int32_t*) buffer) = OSSwapHostToBigInt32(offset);
 203         WriteData(buffer, 4);
 204 }
 205
 206
 207
 208 void SharedMemoryServer::WriteData(const void* data, SegmentOffsetType length)
 209 {
 210         // figure out where in the buffer we actually need to write the data
 211         // figure out how many bytes we can write without overflowing the buffer
 212         const u_int8_t* dp = (const u_int8_t*) data;
 213         SegmentOffsetType bytesToEnd = int_cast<ptrdiff_t, SegmentOffsetType>(mDataMax - mDataPtr);
 214
 215         // figure out how many bytes we can write
 216         SegmentOffsetType bytesToWrite = (length <= bytesToEnd) ? length : bytesToEnd;
 217
 218         // move the first part of the data, making sure to skip the producer pointer
 219         memcpy (mDataPtr, dp, bytesToWrite);
 220         mDataPtr += bytesToWrite;
 221         dp += bytesToWrite;
 222
 223         // deduct the bytes just written
 224         length -= bytesToWrite;
 225
 226         if (length != 0) // did we wrap around?
 227         {
 228                 mDataPtr = mDataArea;
 229                 memcpy (mDataPtr, dp, length);
 230                 mDataPtr += length;
 231         }
 232 }