Commit cb477557 authored Sep 01, 2020 by Zeng Tao Committed by Thomas Gleixner Oct 26, 2020

time: Prevent undefined behaviour in timespec64_to_ns()



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 bd40a175 ("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: 361a3bf0 ("time64: Add time64.h header and define struct timespec64")
Signed-off-by: Zeng Tao <prime.zeng@hisilicon.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/1598952616-6416-1-git-send-email-prime.zeng@hisilicon.com

parent 9010e387

include/linux/time64.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -124,6 +124,10 @@ static inline bool timespec64_valid_settod(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;
		}

kernel/time/itimer.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -172,10 +172,6 @@ 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 = timespec64_to_ns(&value->it_value);
		ninterval = timespec64_to_ns(&value->it_interval);

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