dbghelp: Prevent huge minidumps by ensuring the memory range is clamped.

dlls/dbghelp/minidump.c

@@ -119,20 +119,50 @@ static void fetch_thread_stack(struct dump_context* dc, const void* teb_addr,
     {
 #ifdef __i386__
         /* limiting the stack dumping to the size actually used */
-        if (ctx->Esp)
-            mmd->StartOfMemoryRange = (ctx->Esp - 4);
+        if (ctx->Esp){
+
+            /* make sure ESP is within the established range of the stack.  It could have
+               been clobbered by whatever caused the original exception. */
+            if (ctx->Esp - 4 < (ULONG_PTR)tib.StackLimit || ctx->Esp - 4 > (ULONG_PTR)tib.StackBase)
+                mmd->StartOfMemoryRange = (ULONG_PTR)tib.StackLimit;
+
+            else
+                mmd->StartOfMemoryRange = (ctx->Esp - 4);
+        }
+
         else
             mmd->StartOfMemoryRange = (ULONG_PTR)tib.StackLimit;
+
 #elif defined(__powerpc__)
-        if (ctx->Iar)
-            mmd->StartOfMemoryRange = ctx->Iar - 4;
+        if (ctx->Iar){
+
+            /* make sure IAR is within the established range of the stack.  It could have
+               been clobbered by whatever caused the original exception. */
+            if (ctx->Iar - 4 < (ULONG_PTR)tib.StackLimit || ctx->Iar - 4 > (ULONG_PTR)tib.StackBase)
+                mmd->StartOfMemoryRange = (ULONG_PTR)tib.StackLimit;
+
+            else
+                mmd->StartOfMemoryRange = (ctx->Iar - 4);
+        }
+
         else
             mmd->StartOfMemoryRange = (ULONG_PTR)tib.StackLimit;
+
 #elif defined(__x86_64__)
-        if (ctx->Rsp)
-            mmd->StartOfMemoryRange = (ctx->Rsp - 8);
+        if (ctx->Rsp){
+
+            /* make sure RSP is within the established range of the stack.  It could have
+               been clobbered by whatever caused the original exception. */
+            if (ctx->Rsp - 8 < (ULONG_PTR)tib.StackLimit || ctx->Rsp - 8 > (ULONG_PTR)tib.StackBase)
+                mmd->StartOfMemoryRange = (ULONG_PTR)tib.StackLimit;
+
+            else
+                mmd->StartOfMemoryRange = (ctx->Rsp - 8);
+        }
+
         else
             mmd->StartOfMemoryRange = (ULONG_PTR)tib.StackLimit;
+
 #else
 #error unsupported CPU
 #endif