[NET]: Fix packet timestamping.

I've found the problem in general.  It affects any 64-bit
architecture.  The problem occurs when you change the system time.

Suppose that when you boot your system clock is forward by a day.
This gets recorded down in skb_tv_base.  You then wind the clock back
by a day.  From that point onwards the offset will be negative which
essentially overflows the 32-bit variables they're stored in.

In fact, why don't we just store the real time stamp in those 32-bit
variables? After all, we're not going to overflow for quite a while
yet.

When we do overflow, we'll need a better solution of course.

Signed-off-by: Herbert Xu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

include/linux/skbuff.h

@@ -155,8 +155,6 @@ struct skb_shared_info {
 #define SKB_DATAREF_SHIFT 16
 #define SKB_DATAREF_MASK ((1 << SKB_DATAREF_SHIFT) - 1)
 
-extern struct timeval skb_tv_base;
-
 struct skb_timeval {
 	u32	off_sec;
 	u32	off_usec;
@@ -175,7 +173,7 @@ enum {
  *	@prev: Previous buffer in list
  *	@list: List we are on
  *	@sk: Socket we are owned by
- *	@tstamp: Time we arrived stored as offset to skb_tv_base
+ *	@tstamp: Time we arrived
  *	@dev: Device we arrived on/are leaving by
  *	@input_dev: Device we arrived on
  *	@h: Transport layer header
@@ -1255,10 +1253,6 @@ static inline void skb_get_timestamp(const struct sk_buff *skb, struct timeval *
 {
 	stamp->tv_sec  = skb->tstamp.off_sec;
 	stamp->tv_usec = skb->tstamp.off_usec;
-	if (skb->tstamp.off_sec) {
-		stamp->tv_sec  += skb_tv_base.tv_sec;
-		stamp->tv_usec += skb_tv_base.tv_usec;
-	}
 }
 
 /**
@@ -1272,8 +1266,8 @@ static inline void skb_get_timestamp(const struct sk_buff *skb, struct timeval *
  */
 static inline void skb_set_timestamp(struct sk_buff *skb, const struct timeval *stamp)
 {
-	skb->tstamp.off_sec  = stamp->tv_sec - skb_tv_base.tv_sec;
-	skb->tstamp.off_usec = stamp->tv_usec - skb_tv_base.tv_usec;
+	skb->tstamp.off_sec  = stamp->tv_sec;
+	skb->tstamp.off_usec = stamp->tv_usec;
 }
 
 extern void __net_timestamp(struct sk_buff *skb);

net/core/skbuff.c

@@ -71,8 +71,6 @@
 static kmem_cache_t *skbuff_head_cache __read_mostly;
 static kmem_cache_t *skbuff_fclone_cache __read_mostly;
 
-struct timeval __read_mostly skb_tv_base;
-
 /*
  *	Keep out-of-line to prevent kernel bloat.
  *	__builtin_return_address is not used because it is not always
@@ -1708,8 +1706,6 @@ void __init skb_init(void)
 						NULL, NULL);
 	if (!skbuff_fclone_cache)
 		panic("cannot create skbuff cache");
-
-	do_gettimeofday(&skb_tv_base);
 }
 
 EXPORT_SYMBOL(___pskb_trim);
@@ -1743,4 +1739,3 @@ EXPORT_SYMBOL(skb_prepare_seq_read);
 EXPORT_SYMBOL(skb_seq_read);
 EXPORT_SYMBOL(skb_abort_seq_read);
 EXPORT_SYMBOL(skb_find_text);
-EXPORT_SYMBOL(skb_tv_base);

net/ipv4/netfilter/ip_queue.c

@@ -240,8 +240,8 @@ ipq_build_packet_message(struct ipq_queue_entry *entry, int *errp)
 
 	pmsg->packet_id       = (unsigned long )entry;
 	pmsg->data_len        = data_len;
-	pmsg->timestamp_sec   = skb_tv_base.tv_sec + entry->skb->tstamp.off_sec;
-	pmsg->timestamp_usec  = skb_tv_base.tv_usec + entry->skb->tstamp.off_usec;
+	pmsg->timestamp_sec   = entry->skb->tstamp.off_sec;
+	pmsg->timestamp_usec  = entry->skb->tstamp.off_usec;
 	pmsg->mark            = entry->skb->nfmark;
 	pmsg->hook            = entry->info->hook;
 	pmsg->hw_protocol     = entry->skb->protocol;

net/ipv4/netfilter/ipt_ULOG.c

@@ -225,8 +225,8 @@ static void ipt_ulog_packet(unsigned int hooknum,
 
 	/* copy hook, prefix, timestamp, payload, etc. */
 	pm->data_len = copy_len;
-	pm->timestamp_sec = skb_tv_base.tv_sec + skb->tstamp.off_sec;
-	pm->timestamp_usec = skb_tv_base.tv_usec + skb->tstamp.off_usec;
+	pm->timestamp_sec = skb->tstamp.off_sec;
+	pm->timestamp_usec = skb->tstamp.off_usec;
 	pm->mark = skb->nfmark;
 	pm->hook = hooknum;
 	if (prefix != NULL)

net/ipv6/netfilter/ip6_queue.c

@@ -238,8 +238,8 @@ ipq_build_packet_message(struct ipq_queue_entry *entry, int *errp)
 
 	pmsg->packet_id       = (unsigned long )entry;
 	pmsg->data_len        = data_len;
-	pmsg->timestamp_sec   = skb_tv_base.tv_sec + entry->skb->tstamp.off_sec;
-	pmsg->timestamp_usec  = skb_tv_base.tv_usec + entry->skb->tstamp.off_usec;
+	pmsg->timestamp_sec   = entry->skb->tstamp.off_sec;
+	pmsg->timestamp_usec  = entry->skb->tstamp.off_usec;
 	pmsg->mark            = entry->skb->nfmark;
 	pmsg->hook            = entry->info->hook;
 	pmsg->hw_protocol     = entry->skb->protocol;

net/netfilter/nfnetlink_log.c

@@ -494,8 +494,8 @@ __build_packet_message(struct nfulnl_instance *inst,
 	if (skb->tstamp.off_sec) {
 		struct nfulnl_msg_packet_timestamp ts;
 
-		ts.sec = cpu_to_be64(skb_tv_base.tv_sec + skb->tstamp.off_sec);
-		ts.usec = cpu_to_be64(skb_tv_base.tv_usec + skb->tstamp.off_usec);
+		ts.sec = cpu_to_be64(skb->tstamp.off_sec);
+		ts.usec = cpu_to_be64(skb->tstamp.off_usec);
 
 		NFA_PUT(inst->skb, NFULA_TIMESTAMP, sizeof(ts), &ts);
 	}

net/netfilter/nfnetlink_queue.c

@@ -492,8 +492,8 @@ nfqnl_build_packet_message(struct nfqnl_instance *queue,
 	if (entry->skb->tstamp.off_sec) {
 		struct nfqnl_msg_packet_timestamp ts;
 
-		ts.sec = cpu_to_be64(skb_tv_base.tv_sec + entry->skb->tstamp.off_sec);
-		ts.usec = cpu_to_be64(skb_tv_base.tv_usec + entry->skb->tstamp.off_usec);
+		ts.sec = cpu_to_be64(entry->skb->tstamp.off_sec);
+		ts.usec = cpu_to_be64(entry->skb->tstamp.off_usec);
 
 		NFA_PUT(skb, NFQA_TIMESTAMP, sizeof(ts), &ts);
 	}

net/packet/af_packet.c

@@ -654,8 +654,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
 		__net_timestamp(skb);
 		sock_enable_timestamp(sk);
 	}
-	h->tp_sec = skb_tv_base.tv_sec + skb->tstamp.off_sec;
-	h->tp_usec = skb_tv_base.tv_usec + skb->tstamp.off_usec;
+	h->tp_sec = skb->tstamp.off_sec;
+	h->tp_usec = skb->tstamp.off_usec;
 
 	sll = (struct sockaddr_ll*)((u8*)h + TPACKET_ALIGN(sizeof(*h)));
 	sll->sll_halen = 0;