[NETFILTER]: xt_time: fix failure to match on Sundays

From: Andrew Schulman <[e-mail]>

xt_time_match() in net/netfilter/xt_time.c in kernel 2.6.24 never
matches on Sundays. On my host I have a rule like

iptables -A OUTPUT -m time --weekdays Sun -j REJECT

and it never matches. The problem is in localtime_2(), which uses

r->weekday = (4 + r->dse) % 7;

to map the epoch day onto a weekday in {0,...,6}. In particular this
gives 0 for Sundays. But 0 has to be wrong; a weekday of 0 can never
match. xt_time_match() has

if (!(info->weekdays_match & (1 << current_time.weekday)))
return false;

and when current_time.weekday = 0, the result of the & is always
zero, even when info->weekdays_match = XT_TIME_ALL_WEEKDAYS = 0xFE.

Signed-off-by: Jan Engelhardt <[e-mail]>
Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/netfilter/xt_time.c

···
 	 */
 	r->dse = time / 86400;
 
-	/* 1970-01-01 (w=0) was a Thursday (4). */
-	r->weekday = (4 + r->dse) % 7;
+	/*
+	 * 1970-01-01 (w=0) was a Thursday (4).
+	 * -1 and +1 map Sunday properly onto 7.
+	 */
+	r->weekday = (4 + r->dse - 1) % 7 + 1;
 }
 
 static void localtime_3(struct xtm *r, time_t time)