From d040c8b8a80ffff8c45226d00c71fb63595d11f6 Mon Sep 17 00:00:00 2001
From: zach <zach@dylibso.com>
Date: Mon, 18 Sep 2023 11:23:36 -0700
Subject: [PATCH] fix(kernel): avoid allocating 0-length blocks (#465)

Fixes an issue where the kernel was able to allocate empty blocks,
causing some weird memory issues.
---
 kernel/src/lib.rs               |   6 ++++++
 runtime/src/current_plugin.rs   |   6 ++++++
 runtime/src/extism-runtime.wasm | Bin 2694 -> 2725 bytes
 3 files changed, 12 insertions(+)

diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index 287fe90..d9de25f 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -310,6 +310,9 @@ impl MemoryBlock {
 /// Allocate a block of memory and return the offset
 #[no_mangle]
 pub unsafe fn extism_alloc(n: Length) -> Pointer {
+    if n == 0 {
+        return 0;
+    }
     let region = MemoryRoot::new();
     let block = region.alloc(n);
     match block {
@@ -321,6 +324,9 @@ pub unsafe fn extism_alloc(n: Length) -> Pointer {
 /// Free allocated memory
 #[no_mangle]
 pub unsafe fn extism_free(p: Pointer) {
+    if p == 0 {
+        return;
+    }
     let block = MemoryRoot::new().find_block(p);
     if let Some(block) = block {
         block.free();
diff --git a/runtime/src/current_plugin.rs b/runtime/src/current_plugin.rs
index 9375d56..bf3dc31 100644
--- a/runtime/src/current_plugin.rs
+++ b/runtime/src/current_plugin.rs
@@ -125,6 +125,12 @@ impl CurrentPlugin {
     }
 
     pub fn memory_alloc(&mut self, n: u64) -> Result<MemoryHandle, Error> {
+        if n == 0 {
+            return Ok(MemoryHandle {
+                offset: 0,
+                length: 0,
+            });
+        }
         let (linker, mut store) = self.linker_and_store();
         let output = &mut [Val::I64(0)];
         if let Some(f) = linker.get(&mut store, "env", "extism_alloc") {
diff --git a/runtime/src/extism-runtime.wasm b/runtime/src/extism-runtime.wasm
index b252b6fb46c3d151bb749bd2453eb9d9dc72ec3c..67db36261bd9f553fad7d4499d7523344ef3caad 100755
GIT binary patch
delta 427
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delta 389
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