Bug 1461421 Use OffsetOf to calculate the location of parameters_ rather than making assumptions about the parent class r=bobowen

MozReview-Commit-ID: D7REZiAIMpN

--HG--
extra : rebase_source : 5b320ee658589feec6d95b01448def7eb0a56b69

security/sandbox/chromium/sandbox/win/src/crosscall_params.h

@@ -60,6 +60,7 @@ union MultiType {
 //  - Add another Callback typedef to Dispatcher.
 //  - Add another case to the switch on SharedMemIPCServer::InvokeCallback.
 //  - Add another case to the switch in GetActualAndMaxBufferSize
+//  - Add another case to the switch in GetMinDeclaredActualCallParamsSize
 const int kMaxIpcParams = 9;
 
 // Contains the information about a parameter in the ipc buffer.
@@ -276,6 +277,8 @@ class ActualCallParams : public CrossCallParams {
   char parameters_[BLOCK_SIZE - sizeof(CrossCallParams)
                    - sizeof(ParamInfo) * (NUMBER_PARAMS + 1)];
   DISALLOW_COPY_AND_ASSIGN(ActualCallParams);
+
+  friend uint32_t GetMinDeclaredActualCallParamsSize(uint32_t param_count);
 };
 
 static_assert(sizeof(ActualCallParams<1, 1024>) == 1024, "bad size buffer");

security/sandbox/chromium/sandbox/win/src/crosscall_server.cc

@@ -27,20 +27,21 @@ const size_t kMaxBufferSize = sandbox::kIPCChannelSize;
 
 namespace sandbox {
 
+// The template types are used to calculate the maximum expected size.
+typedef ActualCallParams<0, kMaxBufferSize> ActualCP0;
+typedef ActualCallParams<1, kMaxBufferSize> ActualCP1;
+typedef ActualCallParams<2, kMaxBufferSize> ActualCP2;
+typedef ActualCallParams<3, kMaxBufferSize> ActualCP3;
+typedef ActualCallParams<4, kMaxBufferSize> ActualCP4;
+typedef ActualCallParams<5, kMaxBufferSize> ActualCP5;
+typedef ActualCallParams<6, kMaxBufferSize> ActualCP6;
+typedef ActualCallParams<7, kMaxBufferSize> ActualCP7;
+typedef ActualCallParams<8, kMaxBufferSize> ActualCP8;
+typedef ActualCallParams<9, kMaxBufferSize> ActualCP9;
+
 // Returns the actual size for the parameters in an IPC buffer. Returns
 // zero if the |param_count| is zero or too big.
 uint32_t GetActualBufferSize(uint32_t param_count, void* buffer_base) {
-  // The template types are used to calculate the maximum expected size.
-  typedef ActualCallParams<1, kMaxBufferSize> ActualCP1;
-  typedef ActualCallParams<2, kMaxBufferSize> ActualCP2;
-  typedef ActualCallParams<3, kMaxBufferSize> ActualCP3;
-  typedef ActualCallParams<4, kMaxBufferSize> ActualCP4;
-  typedef ActualCallParams<5, kMaxBufferSize> ActualCP5;
-  typedef ActualCallParams<6, kMaxBufferSize> ActualCP6;
-  typedef ActualCallParams<7, kMaxBufferSize> ActualCP7;
-  typedef ActualCallParams<8, kMaxBufferSize> ActualCP8;
-  typedef ActualCallParams<9, kMaxBufferSize> ActualCP9;
-
   // Retrieve the actual size and the maximum size of the params buffer.
   switch (param_count) {
     case 0:
@@ -68,6 +69,35 @@ uint32_t GetActualBufferSize(uint32_t param_count, void* buffer_base) {
   }
 }
 
+// Returns the minimum size for the parameters in an IPC buffer. Returns
+// zero if the |param_count| is less than zero or too big.
+uint32_t GetMinDeclaredActualCallParamsSize(uint32_t param_count) {
+  switch (param_count) {
+    case 0:
+      return offsetof(ActualCP0, parameters_);
+    case 1:
+      return offsetof(ActualCP1, parameters_);
+    case 2:
+      return offsetof(ActualCP2, parameters_);
+    case 3:
+      return offsetof(ActualCP3, parameters_);
+    case 4:
+      return offsetof(ActualCP4, parameters_);
+    case 5:
+      return offsetof(ActualCP5, parameters_);
+    case 6:
+      return offsetof(ActualCP6, parameters_);
+    case 7:
+      return offsetof(ActualCP7, parameters_);
+    case 8:
+      return offsetof(ActualCP8, parameters_);
+    case 9:
+      return offsetof(ActualCP9, parameters_);
+    default:
+      return 0;
+  }
+}
+
 // Verifies that the declared sizes of an IPC buffer are within range.
 bool IsSizeWithinRange(uint32_t buffer_size,
                        uint32_t min_declared_size,
@@ -137,8 +167,7 @@ CrossCallParamsEx* CrossCallParamsEx::CreateFromBuffer(void* buffer_base,
     // Check against the minimum size given the number of stated params
     // if too small we bail out.
     param_count = call_params->GetParamsCount();
-    min_declared_size = sizeof(CrossCallParams) +
+    min_declared_size = GetMinDeclaredActualCallParamsSize(param_count);
-                        ((param_count + 1) * sizeof(ParamInfo));
 
     // Retrieve the declared size which if it fails returns 0.
     declared_size = GetActualBufferSize(param_count, buffer_base);
@@ -157,8 +186,7 @@ CrossCallParamsEx* CrossCallParamsEx::CreateFromBuffer(void* buffer_base,
     // should be actually read.
     _ReadWriteBarrier();
 
-    min_declared_size = sizeof(CrossCallParams) +
+    min_declared_size = GetMinDeclaredActualCallParamsSize(param_count);
-                        ((param_count + 1) * sizeof(ParamInfo));
 
     // Check that the copied buffer is still valid.
     if (copied_params->GetParamsCount() != param_count ||