ppp: Use a real SKB control block in fragmentation engine.

Do this instead of subverting fields in skb proper.

The macros that could very easily match variable or function
names were also just asking for trouble.
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ppp_generic.c

@@ -1547,9 +1547,11 @@ ppp_channel_push(struct channel *pch)
  * Receive-side routines.
  */
 
-/* misuse a few fields of the skb for MP reconstruction */
-#define sequence	priority
-#define BEbits		cb[0]
+struct ppp_mp_skb_parm {
+	u32		sequence;
+	u8		BEbits;
+};
+#define PPP_MP_CB(skb)	((struct ppp_mp_skb_parm *)((skb)->cb))
 
 static inline void
 ppp_do_recv(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
@@ -1878,13 +1880,13 @@ ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
 		seq = (skb->data[3] << 16) | (skb->data[4] << 8)| skb->data[5];
 		mask = 0xffffff;
 	}
-	skb->BEbits = skb->data[2];
+	PPP_MP_CB(skb)->BEbits = skb->data[2];
 	skb_pull(skb, mphdrlen);	/* pull off PPP and MP headers */
 
 	/*
 	 * Do protocol ID decompression on the first fragment of each packet.
 	 */
-	if ((skb->BEbits & B) && (skb->data[0] & 1))
+	if ((PPP_MP_CB(skb)->BEbits & B) && (skb->data[0] & 1))
 		*skb_push(skb, 1) = 0;
 
 	/*
@@ -1896,7 +1898,7 @@ ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
 		seq += mask + 1;
 	else if ((int)(seq - ppp->minseq) > (int)(mask >> 1))
 		seq -= mask + 1;	/* should never happen */
-	skb->sequence = seq;
+	PPP_MP_CB(skb)->sequence = seq;
 	pch->lastseq = seq;
 
 	/*
@@ -1932,8 +1934,8 @@ ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
 	   before the start of the queue. */
 	if (skb_queue_len(&ppp->mrq) >= PPP_MP_MAX_QLEN) {
 		struct sk_buff *mskb = skb_peek(&ppp->mrq);
-		if (seq_before(ppp->minseq, mskb->sequence))
-			ppp->minseq = mskb->sequence;
+		if (seq_before(ppp->minseq, PPP_MP_CB(mskb)->sequence))
+			ppp->minseq = PPP_MP_CB(mskb)->sequence;
 	}
 
 	/* Pull completed packets off the queue and receive them. */
@@ -1963,12 +1965,12 @@ ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb)
 {
 	struct sk_buff *p;
 	struct sk_buff_head *list = &ppp->mrq;
-	u32 seq = skb->sequence;
+	u32 seq = PPP_MP_CB(skb)->sequence;
 
 	/* N.B. we don't need to lock the list lock because we have the
 	   ppp unit receive-side lock. */
 	skb_queue_walk(list, p) {
-		if (seq_before(seq, p->sequence))
+		if (seq_before(seq, PPP_MP_CB(p)->sequence))
 			break;
 	}
 	__skb_queue_before(list, p, skb);
@@ -1997,22 +1999,22 @@ ppp_mp_reconstruct(struct ppp *ppp)
 	tail = NULL;
 	for (p = head; p != (struct sk_buff *) list; p = next) {
 		next = p->next;
-		if (seq_before(p->sequence, seq)) {
+		if (seq_before(PPP_MP_CB(p)->sequence, seq)) {
 			/* this can't happen, anyway ignore the skb */
 			printk(KERN_ERR "ppp_mp_reconstruct bad seq %u < %u\n",
-			       p->sequence, seq);
+			       PPP_MP_CB(p)->sequence, seq);
 			head = next;
 			continue;
 		}
-		if (p->sequence != seq) {
+		if (PPP_MP_CB(p)->sequence != seq) {
 			/* Fragment `seq' is missing.  If it is after
 			   minseq, it might arrive later, so stop here. */
 			if (seq_after(seq, minseq))
 				break;
 			/* Fragment `seq' is lost, keep going. */
 			lost = 1;
-			seq = seq_before(minseq, p->sequence)?
-				minseq + 1: p->sequence;
+			seq = seq_before(minseq, PPP_MP_CB(p)->sequence)?
+				minseq + 1: PPP_MP_CB(p)->sequence;
 			next = p;
 			continue;
 		}
@@ -2026,7 +2028,7 @@ ppp_mp_reconstruct(struct ppp *ppp)
 		 */
 
 		/* B bit set indicates this fragment starts a packet */
-		if (p->BEbits & B) {
+		if (PPP_MP_CB(p)->BEbits & B) {
 			head = p;
 			lost = 0;
 			len = 0;
@@ -2035,7 +2037,8 @@ ppp_mp_reconstruct(struct ppp *ppp)
 		len += p->len;
 
 		/* Got a complete packet yet? */
-		if (lost == 0 && (p->BEbits & E) && (head->BEbits & B)) {
+		if (lost == 0 && (PPP_MP_CB(p)->BEbits & E) &&
+		    (PPP_MP_CB(head)->BEbits & B)) {
 			if (len > ppp->mrru + 2) {
 				++ppp->dev->stats.rx_length_errors;
 				printk(KERN_DEBUG "PPP: reconstructed packet"
@@ -2061,7 +2064,7 @@ ppp_mp_reconstruct(struct ppp *ppp)
 		 * and we haven't found a complete valid packet yet,
 		 * we can discard up to and including this fragment.
 		 */
-		if (p->BEbits & E)
+		if (PPP_MP_CB(p)->BEbits & E)
 			head = next;
 
 		++seq;
@@ -2071,10 +2074,11 @@ ppp_mp_reconstruct(struct ppp *ppp)
 	if (tail != NULL) {
 		/* If we have discarded any fragments,
 		   signal a receive error. */
-		if (head->sequence != ppp->nextseq) {
+		if (PPP_MP_CB(head)->sequence != ppp->nextseq) {
 			if (ppp->debug & 1)
 				printk(KERN_DEBUG "  missed pkts %u..%u\n",
-				       ppp->nextseq, head->sequence-1);
+				       ppp->nextseq,
+				       PPP_MP_CB(head)->sequence-1);
 			++ppp->dev->stats.rx_dropped;
 			ppp_receive_error(ppp);
 		}
@@ -2083,7 +2087,7 @@ ppp_mp_reconstruct(struct ppp *ppp)
 			/* copy to a single skb */
 			for (p = head; p != tail->next; p = p->next)
 				skb_copy_bits(p, 0, skb_put(skb, p->len), p->len);
-		ppp->nextseq = tail->sequence + 1;
+		ppp->nextseq = PPP_MP_CB(tail)->sequence + 1;
 		head = tail->next;
 	}