time: Always make sure wall_to_monotonic isn't positive

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).

Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Wang YanQing <udknight@gmail.com>
[jstultz: reworded commit message]
Signed-off-by: John Stultz <john.stultz@linaro.org>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index bca3667a2de1f1a221d0fffe0f282137d82fa90e..4cdb771913c8d29b4f61f52bf65d20bf7e3045fe 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -911,6 +911,7 @@ int do_settimeofday64(const struct timespec64 *ts)
        struct timekeeper *tk = &tk_core.timekeeper;
        struct timespec64 ts_delta, xt;
        unsigned long flags;
+       int ret = 0;
 
        if (!timespec64_valid_strict(ts))
                return -EINVAL;
@@ -924,10 +925,15 @@ int do_settimeofday64(const struct timespec64 *ts)
        ts_delta.tv_sec = ts->tv_sec - xt.tv_sec;
        ts_delta.tv_nsec = ts->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));
 
        tk_set_xtime(tk, ts);
-
+out:
        timekeeping_update(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);
 
        write_seqcount_end(&tk_core.seq);
@@ -936,7 +942,7 @@ int do_settimeofday64(const struct timespec64 *ts)
        /* signal hrtimers about time change */
        clock_was_set();
 
-       return 0;
+       return ret;
 }
 EXPORT_SYMBOL(do_settimeofday64);
 
@@ -965,7 +971,8 @@ int timekeeping_inject_offset(struct timespec *ts)
 
        /* 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;
        }