From 43d401288450c187a016a30ca42e8b96d94065c9 Mon Sep 17 00:00:00 2001
From: Murilo Belluzzo <murilo.belluzzo@intel.com>
Date: Mon, 4 Jul 2016 22:31:35 -0300
Subject: [PATCH] AP_HAL: Fix TOCTOU in ByteBuffer::peekiovec()

---
 libraries/AP_HAL/utility/RingBuffer.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/libraries/AP_HAL/utility/RingBuffer.cpp b/libraries/AP_HAL/utility/RingBuffer.cpp
index 76eb30df79..c1350b1655 100644
--- a/libraries/AP_HAL/utility/RingBuffer.cpp
+++ b/libraries/AP_HAL/utility/RingBuffer.cpp
@@ -98,13 +98,15 @@ bool ByteBuffer::advance(uint32_t n)
 
 uint8_t ByteBuffer::peekiovec(ByteBuffer::IoVec iovec[2], uint32_t len)
 {
-    if (len > available()) {
-        len = available();
+    uint32_t n = available();
+
+    if (len > n) {
+        len = n;
     }
     if (len == 0) {
         return 0;
     }
-    uint32_t n;
+
     auto b = readptr(n);
     if (n > len) {
         n = len;