linux-kernel - [PATCH] lib/vdso: guard clockid before building u32 bitmask

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Message-ID: <20260114084529.1676356-1-sun.jian.kdev@gmail.com>
Date: Wed, 14 Jan 2026 16:45:29 +0800
From: Sun Jian <sun.jian.kdev@...il.com>
To: Andy Lutomirski <luto@...nel.org>
Cc: Thomas Gleixner <tglx@...nel.org>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	linux-kernel@...r.kernel.org,
	Sun Jian <sun.jian.kdev@...il.com>
Subject: [PATCH] lib/vdso: guard clockid before building u32 bitmask

__cvdso_clock_gettime_common() and __cvdso_clock_getres_common() build a
u32 bitmask from clockid_t using "1U << clock". This requires the shift
amount to be < 32, otherwise leading to undefined behaviour.

Add a guard to reject out-of-range clockids before building the bitmask.
This avoids undefined shifts and silences sparse "shift too big" warnings.

No functional change intended.

Signed-off-by: Sun Jian <sun.jian.kdev@...il.com>
---
 lib/vdso/gettimeofday.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index 95df0153f05a..eee30f2bc6c6 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -298,6 +298,9 @@ __cvdso_clock_gettime_common(const struct vdso_time_data *vd, clockid_t clock,
 	 * Convert the clockid to a bitmask and use it to check which
 	 * clocks are handled in the VDSO directly.
 	 */
+	if ((u32)clock >= 32)
+		return false;
+
 	msk = 1U << clock;
 	if (likely(msk & VDSO_HRES))
 		vc = &vc[CS_HRES_COARSE];
@@ -440,6 +443,9 @@ bool __cvdso_clock_getres_common(const struct vdso_time_data *vd, clockid_t cloc
 	 * Convert the clockid to a bitmask and use it to check which
 	 * clocks are handled in the VDSO directly.
 	 */
+	if ((u32)clock >= 32)
+		return false;
+
 	msk = 1U << clock;
 	if (msk & (VDSO_HRES | VDSO_RAW)) {
 		/*
-- 
2.43.0