netfilter: xt_time: add support to ignore day transition

Currently, if you want to do something like:
"match Monday, starting 23:00, for two hours"
You need two rules, one for Mon 23:00 to 0:00 and one for Tue 0:00-1:00.

The rule: --weekdays Mo --timestart 23:00  --timestop 01:00

looks correct, but it will first match on monday from midnight to 1 a.m.
and then again for another hour from 23:00 onwards.

This permits userspace to explicitly ignore the day transition and
match for a single, continuous time period instead.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 28 insertions, 1 deletions

diff --git a/include/linux/netfilter/xt_time.h b/include/linux/netfilter/xt_time.h
index 7c37fac576c4..095886019396 100644
--- a/include/linux/netfilter/xt_time.h
+++ b/include/linux/netfilter/xt_time.h
@@ -17,6 +17,9 @@ enum {
         /* Match against local time (instead of UTC) */
         XT_TIME_LOCAL_TZ = 1 << 0,
 
+        /* treat timestart > timestop (e.g. 23:00-01:00) as single period */
+        XT_TIME_CONTIGUOUS = 1 << 1,
+
         /* Shortcuts */
         XT_TIME_ALL_MONTHDAYS = 0xFFFFFFFE,
         XT_TIME_ALL_WEEKDAYS  = 0xFE,
@@ -24,4 +27,6 @@ enum {
         XT_TIME_MAX_DAYTIME   = 24 * 60 * 60 - 1,
 };
 
+#define XT_TIME_ALL_FLAGS (XT_TIME_LOCAL_TZ|XT_TIME_CONTIGUOUS)
+
 #endif /* _XT_TIME_H */
diff --git a/net/netfilter/xt_time.c b/net/netfilter/xt_time.c
index c48975ff8ea2..0ae55a36f492 100644
--- a/net/netfilter/xt_time.c
+++ b/net/netfilter/xt_time.c
@@ -42,6 +42,7 @@ static const u_int16_t days_since_leapyear[] = {
  */
 enum {
         DSE_FIRST = 2039,
+        SECONDS_PER_DAY = 86400,
 };
 static const u_int16_t days_since_epoch[] = {
         /* 2039 - 2030 */
@@ -78,7 +79,7 @@ static inline unsigned int localtime_1(struct xtm *r, time_t time)
         unsigned int v, w;
 
         /* Each day has 86400s, so finding the hour/minute is actually easy. */
-        v         = time % 86400;
+        v         = time % SECONDS_PER_DAY;
         r->second = v % 60;
         w         = v / 60;
         r->minute = w % 60;
@@ -199,6 +200,18 @@ time_mt(const struct sk_buff *skb, struct xt_action_param *par)
                 if (packet_time < info->daytime_start &&
                     packet_time > info->daytime_stop)
                         return false;
+
+                /** if user asked to ignore 'next day', then e.g.
+                 *  '1 PM Wed, August 1st' should be treated
+                 *  like 'Tue 1 PM July 31st'.
+                 *
+                 * This also causes
+                 * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
+                 * Monday 23:00 to Tuesday 01:00.
+                 */
+                if ((info->flags & XT_TIME_CONTIGUOUS) &&
+                     packet_time <= info->daytime_stop)
+                        stamp -= SECONDS_PER_DAY;
         }
 
         localtime_2(&current_time, stamp);
@@ -227,6 +240,15 @@ static int time_mt_check(const struct xt_mtchk_param *par)
                 return -EDOM;
         }
 
+        if (info->flags & ~XT_TIME_ALL_FLAGS) {
+                pr_info("unknown flags 0x%x\n", info->flags & ~XT_TIME_ALL_FLAGS);
+                return -EINVAL;
+        }
+
+        if ((info->flags & XT_TIME_CONTIGUOUS) &&
+             info->daytime_start < info->daytime_stop)
+                return -EINVAL;
+
         return 0;
 }