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    Subject[PATCH 3.18 166/185] rtc: tx4939: avoid unintended sign extension on a 24 bit shift
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Colin Ian King <colin.king@canonical.com>

    [ Upstream commit 347876ad47b9923ce26e686173bbf46581802ffa ]

    The shifting of buf[5] by 24 bits to the left will be promoted to
    a 32 bit signed int and then sign-extended to an unsigned long. If
    the top bit of buf[5] is set then all then all the upper bits sec
    end up as also being set because of the sign-extension. Fix this by
    casting buf[5] to an unsigned long before the shift.

    Detected by CoverityScan, CID#1465292 ("Unintended sign extension")

    Fixes: 0e1492330cd2 ("rtc: add rtc-tx4939 driver")
    Signed-off-by: Colin Ian King <colin.king@canonical.com>
    Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/rtc/rtc-tx4939.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    --- a/drivers/rtc/rtc-tx4939.c
    +++ b/drivers/rtc/rtc-tx4939.c
    @@ -86,7 +86,8 @@ static int tx4939_rtc_read_time(struct d
    for (i = 2; i < 6; i++)
    buf[i] = __raw_readl(&rtcreg->dat);
    spin_unlock_irq(&pdata->lock);
    - sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2];
    + sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) |
    + (buf[3] << 8) | buf[2];
    rtc_time_to_tm(sec, tm);
    return rtc_valid_tm(tm);
    }
    @@ -147,7 +148,8 @@ static int tx4939_rtc_read_alarm(struct
    alrm->enabled = (ctl & TX4939_RTCCTL_ALME) ? 1 : 0;
    alrm->pending = (ctl & TX4939_RTCCTL_ALMD) ? 1 : 0;
    spin_unlock_irq(&pdata->lock);
    - sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2];
    + sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) |
    + (buf[3] << 8) | buf[2];
    rtc_time_to_tm(sec, &alrm->time);
    return rtc_valid_tm(&alrm->time);
    }

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