From 61e16c92ff24bb71b9b7309a9d6d470ee91738bc Mon Sep 17 00:00:00 2001
From: Bartek Nowierski <bartekn@chromium.org>
Date: Wed, 21 Jul 2021 15:01:38 +0000
Subject: [PATCH] [PA] Make GetUsableSize() handle nullptr gracefully

malloc_usable_size() is expected to not crush on NULL and return 0.

Bug: 1221442
Change-Id: I6a3b90dcf3a8ad18114c206d87b98f60d5f50eb1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3042177
Commit-Queue: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#903900}
---

diff --git a/base/allocator/partition_allocator/partition_alloc_unittest.cc b/base/allocator/partition_allocator/partition_alloc_unittest.cc
index c1212011..8863984 100644
--- a/base/allocator/partition_allocator/partition_alloc_unittest.cc
+++ b/base/allocator/partition_allocator/partition_alloc_unittest.cc
@@ -2838,6 +2838,10 @@
   }
 }
 
+TEST_F(PartitionAllocTest, GetUsableSizeNull) {
+  EXPECT_EQ(0ULL, PartitionRoot<ThreadSafe>::GetUsableSize(nullptr));
+}
+
 TEST_F(PartitionAllocTest, GetUsableSize) {
   size_t delta = SystemPageSize() + 1;
   for (size_t size = 1; size <= kMinDirectMappedDownsize; size += delta) {
diff --git a/base/allocator/partition_allocator/partition_root.h b/base/allocator/partition_allocator/partition_root.h
index b72a1d9..baac9525 100644
--- a/base/allocator/partition_allocator/partition_root.h
+++ b/base/allocator/partition_allocator/partition_root.h
@@ -1220,6 +1220,9 @@
 // PartitionAlloc's internal data. Used as malloc_usable_size.
 template <bool thread_safe>
 ALWAYS_INLINE size_t PartitionRoot<thread_safe>::GetUsableSize(void* ptr) {
+  // malloc_usable_size() is expected to handle NULL gracefully and return 0.
+  if (!ptr)
+    return 0;
   auto* slot_span = SlotSpan::FromSlotInnerPtr(ptr);
   auto* root = FromSlotSpan(slot_span);
   return slot_span->GetUsableSize(root);