From a4b0089e989eccdb2921ac9518dd114fbd361ff7 Mon Sep 17 00:00:00 2001
From: svartalf <self@svartalf.info>
Date: Sun, 21 Jun 2020 22:20:43 +0300
Subject: [PATCH] Handle addition overflow when calculating CPU interrupts and
 DPC count stats for Windows (closes #250)

---
 CHANGELOG.md                      |  1 +
 heim-cpu/src/sys/windows/stats.rs | 21 +++++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 83610e38..09bc564a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -38,6 +38,7 @@ for information about previous releases.
 ### Fixed
 
  * `cpu::times` for Linux correctly parses `/proc/stat` (#233)
+ * Handle addition overflow when calculating CPU interrupts stats for Windows (#250)
 
 ## Older versions
 
diff --git a/heim-cpu/src/sys/windows/stats.rs b/heim-cpu/src/sys/windows/stats.rs
index f5f57e19..b461bc8e 100644
--- a/heim-cpu/src/sys/windows/stats.rs
+++ b/heim-cpu/src/sys/windows/stats.rs
@@ -44,20 +44,29 @@ fn system_performance_info() -> Result<(u64, u64)> {
 fn dpc_count() -> Result<u64> {
     let info: Vec<winternl::SYSTEM_INTERRUPT_INFORMATION> = winternl::query_system_information()?;
 
-    let count = info.into_iter().fold(0, |acc, item| acc + item.DpcCount);
+    let count = info.into_iter()
+        .fold(0u64, |acc, item| {
+            // TODO: Log the overflow (`info` level?)
+            acc.overflowing_add(item.DpcCount.into()).0
+        });
 
-    Ok(count.into())
+    Ok(count)
 }
 
 fn interrupts() -> Result<u64> {
     let info: Vec<winternl::SYSTEM_PROCESSOR_PERFORMANCE_INFORMATION> =
         winternl::query_system_information()?;
 
-    let count = info
-        .into_iter()
-        .fold(0, |acc, item| acc + item.InterruptCount);
+    let count = info.into_iter().fold(0u64, |acc, item| {
+        // `InterruptCount` type is `u32` (`ULONG`) and working with `u32`
+        // in here can overflow really quick (see #250).
+        // `u64` will not overflow that fast, but we still want
+        // to handle that case.
+        // TODO: Log the overflow (`info` level?)
+        acc.overflowing_add(item.InterruptCount.into()).0
+    });
 
-    Ok(count.into())
+    Ok(count)
 }
 
 pub async fn stats() -> Result<CpuStats> {