TCMalloc: explicitly prevent int overflow.

third_party/tcmalloc/chromium/src/tcmalloc.cc

 // Copyright (c) 2005, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 122 matching lines @@
 
 #if (defined(_WIN32) && !defined(__CYGWIN__) && !defined(__CYGWIN32__)) && !defined(WIN32_OVERRIDE_ALLOCATORS)
 # define WIN32_DO_PATCHING 1
 #endif
 
 // Some windows file somewhere (at least on cygwin) #define's small (!)
 // For instance, <windows.h> appears to have "#define small char".
 #undef small
 
 using STL_NAMESPACE::max;
+using STL_NAMESPACE::min;
 using STL_NAMESPACE::numeric_limits;
 using STL_NAMESPACE::vector;
 
 #include "libc_override.h"
 
 // __THROW is defined in glibc (via <sys/cdefs.h>).  It means,
 // counter-intuitively, "This function will never throw an exception."
 // It's an optional optimization tool, but we may need to use it to
 // match glibc prototypes.
 #ifndef __THROW    // I guess we're not on a glibc system
@@ skipping 1087 matching lines @@
   AddRoomForMark(&new_size);
   // Get the size of the old entry
   const size_t old_size = GetSizeWithCallback(old_ptr, invalid_get_size_fn);
 
   // Reallocate if the new size is larger than the old size,
   // or if the new size is significantly smaller than the old size.
   // We do hysteresis to avoid resizing ping-pongs:
   //    . If we need to grow, grow to max(new_size, old_size * 1.X)
   //    . Don't shrink unless new_size < old_size * 0.Y
   // X and Y trade-off time for wasted space.  For now we do 1.25 and 0.5.
-  const size_t lower_bound_to_grow = old_size + old_size / 4;
+  const size_t min_growth = min(old_size / 4,
+      (std::numeric_limits<size_t>::max)() - old_size);  // Avoid overflow.
+  const size_t lower_bound_to_grow = old_size + min_growth;
   const size_t upper_bound_to_shrink = old_size / 2;
   if ((new_size > old_size) || (new_size < upper_bound_to_shrink)) {
     // Need to reallocate.
     void* new_ptr = NULL;
 
     if (new_size > old_size && new_size < lower_bound_to_grow) {
       new_ptr = do_malloc_or_cpp_alloc(lower_bound_to_grow);
     }
     ExcludeMarkFromSize(&new_size);  // do_malloc will add space if needed.
     if (new_ptr == NULL) {
@@ skipping 607 matching lines @@
   *mark = ~allocated_mark;  //  Distinctively not allocated.
 }
 
 static void MarkAllocatedRegion(void* ptr) {
   if (ptr == NULL) return;
   MarkType* mark = GetMarkLocation(ptr);
   *mark = GetMarkValue(ptr, mark);
 }
 
 #endif  // TCMALLOC_VALIDATION