netdev - [patch] ppp: potential NULL dereference in ppp_mp

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Date:	Fri, 10 Sep 2010 13:58:10 +0200
From:	Dan Carpenter <error27@...il.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Simon Arlott <simon@...e.lp0.eu>,
	Ben McKeegan <ben@...servers.co.uk>,
	Stephen Hemminger <shemminger@...tta.com>,
	Len Sorensen <lsorense@...lub.uwaterloo.ca>,
	linux-ppp@...r.kernel.org, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [patch] 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.

Signed-off-by: Dan Carpenter <error27@...il.com>
---
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.

diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index 6695a51..736b917 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -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) {
--
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