linux-kernel - [PATCH 5.9 389/391] time: Prevent undefined behaviour in timespec64_to

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Message-Id: <20201103203413.413569789@linuxfoundation.org>
Date:   Tue,  3 Nov 2020 21:37:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Zeng Tao <prime.zeng@...ilicon.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 5.9 389/391] time: Prevent undefined behaviour in timespec64_to_ns()

From: Zeng Tao <prime.zeng@...ilicon.com>

commit cb47755725da7b90fecbb2aa82ac3b24a7adb89b upstream.

UBSAN reports:

Undefined behaviour in ./include/linux/time64.h:127:27
signed integer overflow:
17179869187 * 1000000000 cannot be represented in type 'long long int'
Call Trace:
 timespec64_to_ns include/linux/time64.h:127 [inline]
 set_cpu_itimer+0x65c/0x880 kernel/time/itimer.c:180
 do_setitimer+0x8e/0x740 kernel/time/itimer.c:245
 __x64_sys_setitimer+0x14c/0x2c0 kernel/time/itimer.c:336
 do_syscall_64+0xa1/0x540 arch/x86/entry/common.c:295

Commit bd40a175769d ("y2038: itimer: change implementation to timespec64")
replaced the original conversion which handled time clamping correctly with
timespec64_to_ns() which has no overflow protection.

Fix it in timespec64_to_ns() as this is not necessarily limited to the
usage in itimers.

[ tglx: Added comment and adjusted the fixes tag ]

Fixes: 361a3bf00582 ("time64: Add time64.h header and define struct timespec64")
Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Arnd Bergmann <arnd@...db.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/1598952616-6416-1-git-send-email-prime.zeng@hisilicon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/time64.h |    4 ++++
 kernel/time/itimer.c   |    4 ----
 2 files changed, 4 insertions(+), 4 deletions(-)

--- a/include/linux/time64.h
+++ b/include/linux/time64.h
@@ -124,6 +124,10 @@ static inline bool timespec64_valid_sett
  */
 static inline s64 timespec64_to_ns(const struct timespec64 *ts)
 {
+	/* Prevent multiplication overflow */
+	if ((unsigned long long)ts->tv_sec >= KTIME_SEC_MAX)
+		return KTIME_MAX;
+
 	return ((s64) ts->tv_sec * NSEC_PER_SEC) + ts->tv_nsec;
 }
 
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -172,10 +172,6 @@ static void set_cpu_itimer(struct task_s
 	u64 oval, nval, ointerval, ninterval;
 	struct cpu_itimer *it = &tsk->signal->it[clock_id];
 
-	/*
-	 * Use the to_ktime conversion because that clamps the maximum
-	 * value to KTIME_MAX and avoid multiplication overflows.
-	 */
 	nval = timespec64_to_ns(&value->it_value);
 	ninterval = timespec64_to_ns(&value->it_interval);