From: Wang YanQing udknight@gmail.com

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).

Change-Id: I19acf5df5cc34dd388de0dc633723fe73adc077e 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] [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] Signed-off-by: John Stultz john.stultz@linaro.org Signed-off-by: Harsh Shandilya msfjarvis@gmail.com --- kernel/time/timekeeping.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 07b1c31898bd..caece7c8e44c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -713,6 +713,7 @@ int do_settimeofday(const struct timespec *tv) 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; @@ -726,11 +727,16 @@ int do_settimeofday(const struct timespec *tv) 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); @@ -739,7 +745,7 @@ int do_settimeofday(const struct timespec *tv) /* signal hrtimers about time change */ clock_was_set();

- return 0; + return ret; } EXPORT_SYMBOL(do_settimeofday);

@@ -768,7 +774,8 @@ 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; }