From 9fdbf585f47501ba19a53fd4bb382d5b533e3fdd Mon Sep 17 00:00:00 2001
From: Nikias Bassen
Date: Fri, 6 Nov 2026 09:39:42 +0100
Subject: bplist: Guard uint64_mul_overflow fallback against division by zero

The portable fallback used when __builtin_umulll_overflow is not
available computed a > UINT64_MAX / b, which divides by zero if b is 0.
No current caller passes 0, but return no overflow in that case so the
helper is safe for any input.
---
 src/bplist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/bplist.c b/src/bplist.c
index 0591526..663a118 100644
--- a/src/bplist.c
+++ b/src/bplist.c
@@ -223,7 +223,7 @@ static uint64_t UINT_TO_HOST(const void* x, uint8_t n)
 static int uint64_mul_overflow(uint64_t a, uint64_t b, uint64_t *res)
 {
     *res = a * b;
-    return (a > UINT64_MAX / b);
+    return (b != 0 && a > UINT64_MAX / b);
 }
 #endif
 
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