Re: [PATCH] rtc: Initialized rtc_time->tm_isdst

From: john stultz
Date: Fri Aug 12 2011 - 19:29:23 EST

On Fri, Aug 12, 2011 at 2:04 PM, Mike Waychison <mikew@xxxxxxxxxx> wrote:
> 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
> rtc_wkalrm.

Thanks for catching this! I've queued this in my tree.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at