[ Upstream commit 7a8e61f8478639072d402a26789055a4a4de8f77 ]
Several people reported testing failures after setting CLOCK_REALTIME close to the limits of the kernel internal representation in nanoseconds, i.e. year 2262.
The failures are exposed in subsequent operations, i.e. when arming timers or when the advancing CLOCK_MONOTONIC makes the calculation of CLOCK_REALTIME overflow into negative space.
Now people start to paper over the underlying problem by clamping calculations to the valid range, but that's just wrong because such workarounds will prevent detection of real issues as well.
It is reasonable to force an upper bound for the various methods of setting CLOCK_REALTIME. Year 2262 is the absolute upper bound. Assume a maximum uptime of 30 years which is plenty enough even for esoteric embedded systems. That results in an upper bound of year 2232 for setting the time.
Once that limit is reached in reality this limit is only a small part of the problem space. But until then this stops people from trying to paper over the problem at the wrong places.
Reported-by: Xiongfeng Wang wangxiongfeng2@huawei.com Reported-by: Hongbo Yao yaohongbo@huawei.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: John Stultz john.stultz@linaro.org Cc: Stephen Boyd sboyd@kernel.org Cc: Miroslav Lichvar mlichvar@redhat.com Cc: Arnd Bergmann arnd@arndb.de Cc: Richard Cochran richardcochran@gmail.com Cc: Peter Zijlstra peterz@infradead.org Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1903231125480.2157@nanos.tec.linut... Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/time64.h | 21 +++++++++++++++++++++ kernel/time/time.c | 2 +- kernel/time/timekeeping.c | 6 +++--- 3 files changed, 25 insertions(+), 4 deletions(-)
diff --git a/include/linux/time64.h b/include/linux/time64.h index 05634afba0db6..4a45aea0f96e9 100644 --- a/include/linux/time64.h +++ b/include/linux/time64.h @@ -41,6 +41,17 @@ struct itimerspec64 { #define KTIME_MAX ((s64)~((u64)1 << 63)) #define KTIME_SEC_MAX (KTIME_MAX / NSEC_PER_SEC)
+/* + * Limits for settimeofday(): + * + * To prevent setting the time close to the wraparound point time setting + * is limited so a reasonable uptime can be accomodated. Uptime of 30 years + * should be really sufficient, which means the cutoff is 2232. At that + * point the cutoff is just a small part of the larger problem. + */ +#define TIME_UPTIME_SEC_MAX (30LL * 365 * 24 *3600) +#define TIME_SETTOD_SEC_MAX (KTIME_SEC_MAX - TIME_UPTIME_SEC_MAX) + static inline int timespec64_equal(const struct timespec64 *a, const struct timespec64 *b) { @@ -108,6 +119,16 @@ static inline bool timespec64_valid_strict(const struct timespec64 *ts) return true; }
+static inline bool timespec64_valid_settod(const struct timespec64 *ts) +{ + if (!timespec64_valid(ts)) + return false; + /* Disallow values which cause overflow issues vs. CLOCK_REALTIME */ + if ((unsigned long long)ts->tv_sec >= TIME_SETTOD_SEC_MAX) + return false; + return true; +} + /** * timespec64_to_ns - Convert timespec64 to nanoseconds * @ts: pointer to the timespec64 variable to be converted diff --git a/kernel/time/time.c b/kernel/time/time.c index 2edb5088a70b6..e7a3b9236f0b5 100644 --- a/kernel/time/time.c +++ b/kernel/time/time.c @@ -171,7 +171,7 @@ int do_sys_settimeofday64(const struct timespec64 *tv, const struct timezone *tz static int firsttime = 1; int error = 0;
- if (tv && !timespec64_valid(tv)) + if (tv && !timespec64_valid_settod(tv)) return -EINVAL;
error = security_settime64(tv, tz); diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index ac5dbf2cd4a21..161b2728ac09e 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1221,7 +1221,7 @@ int do_settimeofday64(const struct timespec64 *ts) unsigned long flags; int ret = 0;
- if (!timespec64_valid_strict(ts)) + if (!timespec64_valid_settod(ts)) return -EINVAL;
raw_spin_lock_irqsave(&timekeeper_lock, flags); @@ -1278,7 +1278,7 @@ static int timekeeping_inject_offset(const struct timespec64 *ts) /* Make sure the proposed value is valid */ tmp = timespec64_add(tk_xtime(tk), *ts); if (timespec64_compare(&tk->wall_to_monotonic, ts) > 0 || - !timespec64_valid_strict(&tmp)) { + !timespec64_valid_settod(&tmp)) { ret = -EINVAL; goto error; } @@ -1527,7 +1527,7 @@ void __init timekeeping_init(void) unsigned long flags;
read_persistent_wall_and_boot_offset(&wall_time, &boot_offset); - if (timespec64_valid_strict(&wall_time) && + if (timespec64_valid_settod(&wall_time) && timespec64_to_ns(&wall_time) > 0) { persistent_clock_exists = true; } else if (timespec64_to_ns(&wall_time) != 0) {