netdev - [PATCH net] netfilter: nf_conntrack_pptp: prevent buffer overflows in debug code

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Date:   Wed, 6 May 2020 13:17:53 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH net] netfilter: nf_conntrack_pptp: prevent buffer overflows
 in debug code

Smatch complains that the value for "cmd" comes from the network and
can't be trusted.  The value is actually checked at the end of these
functions so I just copied that here as well.

Fixes: f09943fefe6b ("[NETFILTER]: nf_conntrack/nf_nat: add PPTP helper port")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 net/netfilter/nf_conntrack_pptp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_pptp.c b/net/netfilter/nf_conntrack_pptp.c
index a971183f11af7..b4dc567f7fb68 100644
--- a/net/netfilter/nf_conntrack_pptp.c
+++ b/net/netfilter/nf_conntrack_pptp.c
@@ -276,7 +276,8 @@ pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
 	typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
 
 	msg = ntohs(ctlh->messageType);
-	pr_debug("inbound control message %s\n", pptp_msg_name[msg]);
+	pr_debug("inbound control message %s\n",
+		 msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0]);
 
 	switch (msg) {
 	case PPTP_START_SESSION_REPLY:
@@ -404,7 +405,8 @@ pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
 	typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
 
 	msg = ntohs(ctlh->messageType);
-	pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
+	pr_debug("outbound control message %s\n",
+		 msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0]);
 
 	switch (msg) {
 	case PPTP_START_SESSION_REQUEST:
-- 
2.26.2