[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 <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 9 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2741c0c55e83..466c879f82b8 100644
--- a/include/linux/skbuff.h
+++ b/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);