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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include <string>
      6 #include <vector>
      7 
      8 #include "sandbox/win/src/crosscall_server.h"
      9 #include "sandbox/win/src/crosscall_params.h"
     10 #include "sandbox/win/src/crosscall_client.h"
     11 #include "base/logging.h"
     12 
     13 // This code performs the ipc message validation. Potential security flaws
     14 // on the ipc are likelier to be found in this code than in the rest of
     15 // the ipc code.
     16 
     17 namespace {
     18 
     19 // The buffer for a message must match the max channel size.
     20 const size_t kMaxBufferSize = sandbox::kIPCChannelSize;
     21 
     22 }
     23 
     24 namespace sandbox {
     25 
     26 // Returns the actual size for the parameters in an IPC buffer. Returns
     27 // zero if the |param_count| is zero or too big.
     28 uint32 GetActualBufferSize(uint32 param_count, void* buffer_base) {
     29   // The template types are used to calculate the maximum expected size.
     30   typedef ActualCallParams<1, kMaxBufferSize> ActualCP1;
     31   typedef ActualCallParams<2, kMaxBufferSize> ActualCP2;
     32   typedef ActualCallParams<3, kMaxBufferSize> ActualCP3;
     33   typedef ActualCallParams<4, kMaxBufferSize> ActualCP4;
     34   typedef ActualCallParams<5, kMaxBufferSize> ActualCP5;
     35   typedef ActualCallParams<6, kMaxBufferSize> ActualCP6;
     36   typedef ActualCallParams<7, kMaxBufferSize> ActualCP7;
     37   typedef ActualCallParams<8, kMaxBufferSize> ActualCP8;
     38   typedef ActualCallParams<9, kMaxBufferSize> ActualCP9;
     39 
     40   // Retrieve the actual size and the maximum size of the params buffer.
     41   switch (param_count) {
     42     case 0:
     43       return 0;
     44     case 1:
     45       return reinterpret_cast<ActualCP1*>(buffer_base)->GetSize();
     46     case 2:
     47       return reinterpret_cast<ActualCP2*>(buffer_base)->GetSize();
     48     case 3:
     49       return reinterpret_cast<ActualCP3*>(buffer_base)->GetSize();
     50     case 4:
     51       return reinterpret_cast<ActualCP4*>(buffer_base)->GetSize();
     52     case 5:
     53       return reinterpret_cast<ActualCP5*>(buffer_base)->GetSize();
     54     case 6:
     55       return reinterpret_cast<ActualCP6*>(buffer_base)->GetSize();
     56     case 7:
     57       return reinterpret_cast<ActualCP7*>(buffer_base)->GetSize();
     58     case 8:
     59       return reinterpret_cast<ActualCP8*>(buffer_base)->GetSize();
     60     case 9:
     61       return reinterpret_cast<ActualCP9*>(buffer_base)->GetSize();
     62     default:
     63       return 0;
     64   }
     65 }
     66 
     67 // Verifies that the declared sizes of an IPC buffer are within range.
     68 bool IsSizeWithinRange(uint32 buffer_size, uint32 min_declared_size,
     69                        uint32 declared_size) {
     70   if ((buffer_size < min_declared_size) ||
     71       (sizeof(CrossCallParamsEx) > min_declared_size)) {
     72     // Minimal computed size bigger than existing buffer or param_count
     73     // integer overflow.
     74     return false;
     75   }
     76 
     77   if ((declared_size > buffer_size) || (declared_size < min_declared_size)) {
     78     // Declared size is bigger than buffer or smaller than computed size
     79     // or param_count is equal to 0 or bigger than 9.
     80     return false;
     81   }
     82 
     83   return true;
     84 }
     85 
     86 CrossCallParamsEx::CrossCallParamsEx()
     87   :CrossCallParams(0, 0) {
     88 }
     89 
     90 // We override the delete operator because the object's backing memory
     91 // is hand allocated in CreateFromBuffer. We don't override the new operator
     92 // because the constructors are private so there is no way to mismatch
     93 // new & delete.
     94 void CrossCallParamsEx::operator delete(void* raw_memory) throw() {
     95   if (NULL == raw_memory) {
     96     // C++ standard allows 'delete 0' behavior.
     97     return;
     98   }
     99   delete[] reinterpret_cast<char*>(raw_memory);
    100 }
    101 
    102 // This function uses a SEH try block so cannot use C++ objects that
    103 // have destructors or else you get Compiler Error C2712. So no DCHECKs
    104 // inside this function.
    105 CrossCallParamsEx* CrossCallParamsEx::CreateFromBuffer(void* buffer_base,
    106                                                        uint32 buffer_size,
    107                                                        uint32* output_size) {
    108   // IMPORTANT: Everything inside buffer_base and derived from it such
    109   // as param_count and declared_size is untrusted.
    110   if (NULL == buffer_base) {
    111     return NULL;
    112   }
    113   if (buffer_size < sizeof(CrossCallParams)) {
    114     return NULL;
    115   }
    116   if (buffer_size > kMaxBufferSize) {
    117     return NULL;
    118   }
    119 
    120   char* backing_mem = NULL;
    121   uint32 param_count = 0;
    122   uint32 declared_size;
    123   uint32 min_declared_size;
    124   CrossCallParamsEx* copied_params = NULL;
    125 
    126   // Touching the untrusted buffer is done under a SEH try block. This
    127   // will catch memory access violations so we don't crash.
    128   __try {
    129     CrossCallParams* call_params =
    130         reinterpret_cast<CrossCallParams*>(buffer_base);
    131 
    132     // Check against the minimum size given the number of stated params
    133     // if too small we bail out.
    134     param_count = call_params->GetParamsCount();
    135     min_declared_size = sizeof(CrossCallParams) +
    136                         ((param_count + 1) * sizeof(ParamInfo));
    137 
    138     // Retrieve the declared size which if it fails returns 0.
    139     declared_size = GetActualBufferSize(param_count, buffer_base);
    140 
    141     if (!IsSizeWithinRange(buffer_size, min_declared_size, declared_size))
    142       return NULL;
    143 
    144     // Now we copy the actual amount of the message.
    145     *output_size = declared_size;
    146     backing_mem = new char[declared_size];
    147     copied_params = reinterpret_cast<CrossCallParamsEx*>(backing_mem);
    148     memcpy(backing_mem, call_params, declared_size);
    149 
    150     // Avoid compiler optimizations across this point. Any value stored in
    151     // memory should be stored for real, and values previously read from memory
    152     // should be actually read.
    153     _ReadWriteBarrier();
    154 
    155     min_declared_size = sizeof(CrossCallParams) +
    156                         ((param_count + 1) * sizeof(ParamInfo));
    157 
    158     // Check that the copied buffer is still valid.
    159     if (copied_params->GetParamsCount() != param_count ||
    160         GetActualBufferSize(param_count, backing_mem) != declared_size ||
    161         !IsSizeWithinRange(buffer_size, min_declared_size, declared_size)) {
    162       delete [] backing_mem;
    163       return NULL;
    164     }
    165 
    166   } __except(EXCEPTION_EXECUTE_HANDLER) {
    167     // In case of a windows exception we know it occurred while touching the
    168     // untrusted buffer so we bail out as is.
    169     delete [] backing_mem;
    170     return NULL;
    171   }
    172 
    173   const char* last_byte = &backing_mem[declared_size];
    174   const char* first_byte = &backing_mem[min_declared_size];
    175 
    176   // Verify here that all and each parameters make sense. This is done in the
    177   // local copy.
    178   for (uint32 ix =0; ix != param_count; ++ix) {
    179     uint32 size = 0;
    180     ArgType type;
    181     char* address = reinterpret_cast<char*>(
    182                         copied_params->GetRawParameter(ix, &size, &type));
    183     if ((NULL == address) ||               // No null params.
    184         (INVALID_TYPE >= type) || (LAST_TYPE <= type) ||  // Unknown type.
    185         (address < backing_mem) ||         // Start cannot point before buffer.
    186         (address < first_byte) ||          // Start cannot point too low.
    187         (address > last_byte) ||           // Start cannot point past buffer.
    188         ((address + size) < address) ||    // Invalid size.
    189         ((address + size) > last_byte)) {  // End cannot point past buffer.
    190       // Malformed.
    191       delete[] backing_mem;
    192       return NULL;
    193     }
    194   }
    195   // The parameter buffer looks good.
    196   return copied_params;
    197 }
    198 
    199 // Accessors to the parameters in the raw buffer.
    200 void* CrossCallParamsEx::GetRawParameter(uint32 index, uint32* size,
    201                                          ArgType* type) {
    202   if (index >= GetParamsCount()) {
    203     return NULL;
    204   }
    205   // The size is always computed from the parameter minus the next
    206   // parameter, this works because the message has an extra parameter slot
    207   *size = param_info_[index].size_;
    208   *type = param_info_[index].type_;
    209 
    210   return param_info_[index].offset_ + reinterpret_cast<char*>(this);
    211 }
    212 
    213 // Covers common case for 32 bit integers.
    214 bool CrossCallParamsEx::GetParameter32(uint32 index, uint32* param) {
    215   uint32 size = 0;
    216   ArgType type;
    217   void* start = GetRawParameter(index, &size, &type);
    218   if ((NULL == start) || (4 != size) || (ULONG_TYPE != type)) {
    219     return false;
    220   }
    221   // Copy the 4 bytes.
    222   *(reinterpret_cast<uint32*>(param)) = *(reinterpret_cast<uint32*>(start));
    223   return true;
    224 }
    225 
    226 bool CrossCallParamsEx::GetParameterVoidPtr(uint32 index, void** param) {
    227   uint32 size = 0;
    228   ArgType type;
    229   void* start = GetRawParameter(index, &size, &type);
    230   if ((NULL == start) || (sizeof(void*) != size) || (VOIDPTR_TYPE != type)) {
    231     return false;
    232   }
    233   *param = *(reinterpret_cast<void**>(start));
    234   return true;
    235 }
    236 
    237 // Covers the common case of reading a string. Note that the string is not
    238 // scanned for invalid characters.
    239 bool CrossCallParamsEx::GetParameterStr(uint32 index, base::string16* string) {
    240   uint32 size = 0;
    241   ArgType type;
    242   void* start = GetRawParameter(index, &size, &type);
    243   if (WCHAR_TYPE != type) {
    244     return false;
    245   }
    246 
    247   // Check if this is an empty string.
    248   if (size == 0) {
    249     *string = L"";
    250     return true;
    251   }
    252 
    253   if ((NULL == start) || ((size % sizeof(wchar_t)) != 0)) {
    254     return false;
    255   }
    256   string->append(reinterpret_cast<wchar_t*>(start), size/(sizeof(wchar_t)));
    257   return true;
    258 }
    259 
    260 bool CrossCallParamsEx::GetParameterPtr(uint32 index, uint32 expected_size,
    261                                         void** pointer) {
    262   uint32 size = 0;
    263   ArgType type;
    264   void* start = GetRawParameter(index, &size, &type);
    265 
    266   if ((size != expected_size) || (INOUTPTR_TYPE != type)) {
    267     return false;
    268   }
    269 
    270   if (NULL == start) {
    271     return false;
    272   }
    273 
    274   *pointer = start;
    275   return true;
    276 }
    277 
    278 void SetCallError(ResultCode error, CrossCallReturn* call_return) {
    279   call_return->call_outcome = error;
    280   call_return->extended_count = 0;
    281 }
    282 
    283 void SetCallSuccess(CrossCallReturn* call_return) {
    284   call_return->call_outcome = SBOX_ALL_OK;
    285 }
    286 
    287 Dispatcher* Dispatcher::OnMessageReady(IPCParams* ipc,
    288                                       CallbackGeneric* callback) {
    289   DCHECK(callback);
    290   std::vector<IPCCall>::iterator it = ipc_calls_.begin();
    291   for (; it != ipc_calls_.end(); ++it) {
    292     if (it->params.Matches(ipc)) {
    293       *callback = it->callback;
    294       return this;
    295     }
    296   }
    297   return NULL;
    298 }
    299 
    300 }  // namespace sandbox
    301