From 85c267afa7ce4697a1231649de815b2556b3950f Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 9 Dec 2019 18:24:41 +0100
Subject: macro: avoid subtraction overflow in ALIGN_POWER2()

---
 src/basic/macro.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/basic/macro.h b/src/basic/macro.h
index 18e5085669..712bb422b1 100644
--- a/src/basic/macro.h
+++ b/src/basic/macro.h
@@ -163,6 +163,11 @@ static inline size_t ALIGN_TO(size_t l, size_t ali) {
 
 /* align to next higher power-of-2 (except for: 0 => 0, overflow => 0) */
 static inline unsigned long ALIGN_POWER2(unsigned long u) {
+
+        /* Avoid subtraction overflow */
+        if (u == 0)
+                return 0;
+
         /* clz(0) is undefined */
         if (u == 1)
                 return 1;
-- 
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