[PATCH 3.18 166/185] rtc: tx4939: avoid unintended sign extension on a 24 bit shift

[Greg Kroah-Hartman]

3.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Colin Ian King <colin.k...@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.k...@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.bell...@bootlin.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@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);
 }