[PATCH] rtc: Initialized rtc_time->tm_isdst

From: Mike Waychison
Date: Fri Aug 12 2011 - 17:05:15 EST

Even though the Linux kernel does not use the tm_isdst field, it is
exposed as part of the ABI. This field can accidentally be left
initialized, which is why we currently memset buffers returned to
userland in rtc_read_time.

There is a case however where the field can return garbage from the
stack though when using the RTC_ALM_READ ioctl on the rtc device. This
ioctl invokes rtc_read_alarm, which is careful to memset the rtc_wkalrm
buffer that is copied to userland, but it then uses a struct copy to
assign to alarm->time given the return value from rtc_ktime_to_tm().

rtc_ktime_to_tm() is implemented by calling rtc_time_to_tm using a
derivative seconds counds from ktime, but rtc_time_to_tm does not assign
a value to ->tm_isdst. This results in garbage from rtc_ktime_to_tm()'s
frame ending up being copied out to userland as part of the returned

Fix this by initializing rtc_time->tm_isdst to 0 in rtc_time_to_tm.

Signed-off-by: Mike Waychison <mikew@xxxxxxxxxx>
drivers/rtc/rtc-lib.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index 075f170..c4cf057 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -85,6 +85,8 @@ void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
time -= tm->tm_hour * 3600;
tm->tm_min = time / 60;
tm->tm_sec = time - tm->tm_min * 60;
+ tm->tm_isdst = 0;


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