replace brk and sbrk with stubs

Pretend that there is never room to grow the heap in order to prevent
usage of these unsafe legacy functions. There are likely no users of
these in practice as it is inherently broken to use them outside of
malloc.

Signed-off-by: anupritaisno1 <www.anuprita804@gmail.com>

libc/bionic/brk.cpp

@@ -29,48 +29,16 @@
 #include <errno.h>
 #include <unistd.h>
 
-#if defined(__LP64__)
-static void* __bionic_brk;
-#else
-void* __bionic_brk; // Accidentally exported by the NDK.
+#if !defined(__LP64__)
+void* __bionic_brk = reinterpret_cast<void*>(-1); // Accidentally exported by the NDK.
 #endif
 
-extern "C" void* __brk(void* __addr);
-
-int brk(void* end_data) {
-  __bionic_brk = __brk(end_data);
-  if (__bionic_brk < end_data) {
-    errno = ENOMEM;
-    return -1;
-  }
-  return 0;
+int brk(void*) {
+  errno = ENOMEM;
+  return -1;
 }
 
-void* sbrk(ptrdiff_t increment) {
-  // Initialize __bionic_brk if necessary.
-  if (__bionic_brk == nullptr) {
-    __bionic_brk = __brk(nullptr);
-  }
-
-  // Don't ask the kernel if we already know the answer.
-  if (increment == 0) {
-    return __bionic_brk;
-  }
-
-  // Avoid overflow.
-  uintptr_t old_brk = reinterpret_cast<uintptr_t>(__bionic_brk);
-  if ((increment > 0 && static_cast<uintptr_t>(increment) > (UINTPTR_MAX - old_brk)) ||
-      (increment < 0 && static_cast<uintptr_t>(-increment) > old_brk)) {
-    errno = ENOMEM;
-    return reinterpret_cast<void*>(-1);
-  }
-
-  void* desired_brk = reinterpret_cast<void*>(old_brk + increment);
-  __bionic_brk = __brk(desired_brk);
-  if (__bionic_brk < desired_brk) {
-    errno = ENOMEM;
-    return reinterpret_cast<void*>(-1);
-  }
-
-  return reinterpret_cast<void*>(old_brk);
+void* sbrk(ptrdiff_t) {
+  errno = ENOMEM;
+  return reinterpret_cast<void*>(-1);
 }