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    Subject[PATCH 4.19 002/101] time: Prevent undefined behaviour in timespec64_to_ns()
    Date
    From: Zeng Tao <prime.zeng@hisilicon.com>

    [ 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@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
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 4a45aea0f96e9..8dbdf6cae3e8b 100644
    --- a/include/linux/time64.h
    +++ b/include/linux/time64.h
    @@ -138,6 +138,10 @@ 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;
    }

    diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
    index 9a65713c83093..2e2b335ef1018 100644
    --- a/kernel/time/itimer.c
    +++ b/kernel/time/itimer.c
    @@ -154,10 +154,6 @@ 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


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