[PATCH 4.14 04/85] time: Prevent undefined behaviour in timespec64_to_ns()

[Greg Kroah-Hartman]

From: Zeng Tao <prime.zeng@xxxxxxxxxxxxx>

[ Upstream commit cb47755725da7b90fecbb2aa82ac3b24a7adb89b ]

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@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/1598952616-6416-1-git-send-email-prime.zeng@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/time64.h | 4 ++++
 kernel/time/itimer.c   | 4 ----
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/time64.h b/include/linux/time64.h
index ad33260618f76..99ab4a686c301 100644
--- a/include/linux/time64.h
+++ b/include/linux/time64.h
@@ -189,6 +189,10 @@ static inline bool timespec64_valid_strict(const struct timespec64 *ts)
  */
 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;
 }
 
diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
index f26acef5d7b48..7f718565507b5 100644
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -153,10 +153,6 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
 	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 = ktime_to_ns(timeval_to_ktime(value->it_value));
 	ninterval = ktime_to_ns(timeval_to_ktime(value->it_interval));
 
-- 
2.27.0