ppp: potential NULL dereference in ppp_mp_explode()

Smatch complains because we check whether "pch->chan" is NULL and then dereference it unconditionally on the next line. Partly the reason this bug was introduced is because code was too complicated. I've simplified it a little.

---
Compile tested only. Perhaps it would be better to set pch->speed to zero? The comments say that zero implies the speed hasn't been set.

index 6695a51..736b917 100644
@@ -1314,8 +1314,13 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
 	hdrlen = (ppp->flags & SC_MP_XSHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;
 	i = 0;
 	list_for_each_entry(pch, &ppp->channels, clist) {
-		navail += pch->avail = (pch->chan != NULL);
-		pch->speed = pch->chan->speed;
+		if (pch->chan) {
+			pch->avail = 1;
+			navail++;
+			pch->speed = pch->chan->speed;
+		} else {
+			pch->avail = 0;
+		}
 		if (pch->avail) {
 			if (skb_queue_empty(&pch->file.xq) ||
 				!pch->had_frag) {

From: Dan Carpenter <[email protected]>
Date: Fri, 10 Sep 2010 13:58:10 +0200

I think how you've fixed it is OK, actually this whole MP rewrite could use some more auditing :-)

Applied, thanks Dan.