From eadfbb13185a94a30d87c52eb50e83fcec8e0d52 Mon Sep 17 00:00:00 2001
From: Feoramund <161657516+Feoramund@users.noreply.github.com>
Date: Tue, 28 May 2024 19:49:56 -0400
Subject: [PATCH] Forbid singleton allocations from shrinking their block
 offset

---
 core/mem/rollback_stack_allocator.odin | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/core/mem/rollback_stack_allocator.odin b/core/mem/rollback_stack_allocator.odin
index a3f6647cf..b86f514ec 100644
--- a/core/mem/rollback_stack_allocator.odin
+++ b/core/mem/rollback_stack_allocator.odin
@@ -155,7 +155,11 @@ rb_resize :: proc(stack: ^Rollback_Stack, ptr: rawptr, old_size, size, alignment
 			assert(block.offset >= cast(uintptr)old_size, "Rollback Stack Allocator received invalid `old_size`.")
 
 			if block.offset + cast(uintptr)size - cast(uintptr)old_size < cast(uintptr)len(block.buffer) {
-				block.offset += cast(uintptr)size - cast(uintptr)old_size
+				// Prevent singleton allocations from fragmenting by forbidding
+				// them to shrink, removing the possibility of overflow bugs.
+				if len(block.buffer) <= stack.block_size {
+					block.offset += cast(uintptr)size - cast(uintptr)old_size
+				}
 				#no_bounds_check return (cast([^]byte)ptr)[:size], nil
 			}
 		}