linux-kernel - [PATCH] x86/lib: Fix num_digits() signed overflow for INT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20260120094258.41313-1-david.desobry@formalgen.com>
Date: Tue, 20 Jan 2026 10:42:58 +0100
From: David Desobry <david.desobry@...malgen.com>
To: tglx@...nel.org,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com
Cc: x86@...nel.org,
	hpa@...or.com,
	linux-kernel@...r.kernel.org,
	David Desobry <david.desobry@...malgen.com>
Subject: [PATCH] x86/lib: Fix num_digits() signed overflow for INT_MIN

In num_digits(), the negation of the input value "val = -val"
causes undefined behavior when val is INT_MIN, as its absolute
value cannot be represented as a signed 32-bit integer.

This leads to incorrect results (returning 2 instead of 11).
By promoting the value to long long before negation, we ensure
the absolute value is correctly handled.

Signed-off-by: David Desobry <david.desobry@...malgen.com>
---
 arch/x86/lib/misc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/lib/misc.c b/arch/x86/lib/misc.c
index 40b81c338ae5..c975db6ccb9f 100644
--- a/arch/x86/lib/misc.c
+++ b/arch/x86/lib/misc.c
@@ -8,15 +8,16 @@
  */
 int num_digits(int val)
 {
+	long long v = val;
 	long long m = 10;
 	int d = 1;
 
-	if (val < 0) {
+	if (v < 0) {
 		d++;
-		val = -val;
+		v = -v;
 	}
 
-	while (val >= m) {
+	while (v >= m) {
 		m *= 10;
 		d++;
 	}
-- 
2.43.0