Patch "time: Always make sure wall_to_monotonic isn't positive" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

time: Always make sure wall_to_monotonic isn't positive

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
time-always-make-sure-wall_to_monotonic-isn-t-positive.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Wang YanQing <[email protected]>
Date: Tue, 23 Jun 2015 18:38:54 +0800
Subject: time: Always make sure wall_to_monotonic isn't positive

From: Wang YanQing <[email protected]>

commit e1d7ba8735551ed79c7a0463a042353574b96da3 upstream.

Two issues were found on an IMX6 development board without an enabled RTC device(resulting in the boot time and monotonic time being initialized to 0).

Issue 1:exportfs -a generate:
"exportfs: /opt/nfs/arm does not support NFS export"
Issue 2:cat /proc/stat:

       "btime 4294967236"

The same issues can be reproduced on x86 after running the following code:

	int main(void)
	{
	    struct timeval val;
	    int ret;

	    val.tv_sec = 0;
	    val.tv_usec = 0;
	    ret = settimeofday(&val, NULL);
	    return 0;
	}

Two issues are different symptoms of same problem:
The reason is a positive wall_to_monotonic pushes boot time back to the time before Epoch, and getboottime will return negative value.

In symptom 1:
negative boot time cause get_expiry() to overflow time_t when input expire time is 2147483647, then cache_flush() always clears entries just added in ip_map_parse.
In symptom 2:
show_stat() uses "unsigned long" to print negative btime value returned by getboottime.

This patch fix the problem by prohibiting time from being set to a value which would cause a negative boot time. As a result one can't set the CLOCK_REALTIME time prior to (1970 + system uptime).

[msfjarvis: Backport to 3.18 as we are missing the do_settimeofday64 function the upstream commit patches, so we apply the changes to do_settimeofday]

---
 kernel/time/timekeeping.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

@@ -712,6 +712,7 @@ int do_settimeofday(const struct timespe
 	struct timekeeper *tk = &tk_core.timekeeper;
 	struct timespec64 ts_delta, xt, tmp;
 	unsigned long flags;
+	int ret = 0;
 
 	if (!timespec_valid_strict(tv))
 		return -EINVAL;

@@ -725,11 +726,16 @@ int do_settimeofday(const struct timespe
 	ts_delta.tv_sec = tv->tv_sec - xt.tv_sec;
 	ts_delta.tv_nsec = tv->tv_nsec - xt.tv_nsec;
 
+	if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta));
 
 	tmp = timespec_to_timespec64(*tv);
 	tk_set_xtime(tk, &tmp);
-
+out:
 	timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
 
 	write_seqcount_end(&tk_core.seq);

@@ -738,7 +744,7 @@ int do_settimeofday(const struct timespe
 	/* signal hrtimers about time change */
 	clock_was_set();
 
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL(do_settimeofday);
 

@@ -767,7 +773,8 @@ int timekeeping_inject_offset(struct tim
 
 	/* Make sure the proposed value is valid */
 	tmp = timespec64_add(tk_xtime(tk),  ts64);
-	if (!timespec64_valid_strict(&tmp)) {
+	if (timespec64_compare(&tk->wall_to_monotonic, &ts64) > 0 ||
+		!timespec64_valid_strict(&tmp)) {
 		ret = -EINVAL;
 		goto error;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/time-always-make-sure-wall_to_monotonic-isn-t-positive.patch