netdev - [PATCH net-next v2] net: l2tp: fix reading optional fields of L2TPv3

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Message-Id: <20190124074917.31173-1-jian.w.wen@oracle.com>
Date:   Thu, 24 Jan 2019 15:49:17 +0800
From:   Jacob Wen <jian.w.wen@...cle.com>
To:     netdev@...r.kernel.org
Cc:     eric.dumazet@...il.com, g.nault@...halink.fr
Subject: [PATCH net-next v2] net: l2tp: fix reading optional fields of L2TPv3

Use pskb_may_pull() to make sure the optional fields are in skb linear
parts, so we can safely read them later.

It's easy to reproduce the issue with a net driver that supports paged
skb data. Just create a L2TPv3 over IP tunnel and then generates some
network traffic.
Once reproduced, rx err in /sys/kernel/debug/l2tp/tunnels will increase.

Signed-off-by: Jacob Wen <jian.w.wen@...cle.com>
---
Changes in v2:
1. Only fix L2TPv3 to make code simple. 
   To fix both L2TPv3 and L2TPv2, we'd better refactor l2tp_recv_common. 
   It's complicated to do so.
2. Reloading pointers after pskb_may_pull
---
 net/l2tp/l2tp_core.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 26f1d435696a..e9a17c634c1a 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -625,6 +625,20 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 	int offset;
 	u32 ns, nr;
 
+	if (tunnel->version != L2TP_HDR_VER_2) {
+		int opt_len = session->peer_cookie_len +
+			l2tp_get_l2specific_len(session);
+
+		if (opt_len > 0) {
+			int off = ptr - optr;
+
+			if (!pskb_may_pull(skb, off + opt_len))
+				goto discard;
+			optr = skb->data;
+			ptr = optr + off;
+		}
+	}
+
 	/* Parse and check optional cookie */
 	if (session->peer_cookie_len > 0) {
 		if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) {
-- 
2.17.1