Add check to detect double free in linked list allocator

2 files changed, 9 insertions, 1 deletions

diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index 7992b34..e68f0fe 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -42,9 +42,10 @@ namespace teachos::arch::kernel
 
     heap_allocator.deallocate(test, 1024);
 
-    heap_allocator.allocate(1024);  // test 9
+    auto test9 = heap_allocator.allocate(1024);
     auto test10 = heap_allocator.allocate(1024);
     auto test11 = heap_allocator.allocate(1024);
+    heap_allocator.deallocate(test9, 1024);
     auto test12 = heap_allocator.allocate(1024);
     heap_allocator.allocate(1024);  // test 13
     heap_allocator.deallocate(test11, 1024);
diff --git a/arch/x86_64/src/memory/heap/linked_list_allocator.cpp b/arch/x86_64/src/memory/heap/linked_list_allocator.cpp
index 706f43e..f596f27 100644
--- a/arch/x86_64/src/memory/heap/linked_list_allocator.cpp
+++ b/arch/x86_64/src/memory/heap/linked_list_allocator.cpp
@@ -126,6 +126,13 @@ namespace teachos::arch::memory::heap
       return;
     }
 
+    // Check if the block we want to deallocate is contained in the previous block, because if it is it can only mean
+    // that the block has already been deallocated and we therefore attempted a double free.
+    exception_handling::assert(previous_block == nullptr ||
+                                   start_address >=
+                                       (reinterpret_cast<std::size_t>(previous_block) + previous_block->size),
+                               "[Linked List Allocator] Attempted double free detected");
+
     auto const new_block = new (pointer) memory_block(block_size, next_block);
     // If we want to deallocate the first block that is before any other free block, then there exists no previous free
     // block (nullptr). Therefore we have to overwrite the first block instead of overwriting its