netdev - [PATCH net v3] net: l2tp: fix reading optional fields of L2TPv3

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Message-Id: <20190129061813.8097-1-jian.w.wen@oracle.com>
Date:   Tue, 29 Jan 2019 14:18:13 +0800
From:   Jacob Wen <jian.w.wen@...cle.com>
To:     netdev@...r.kernel.org
Cc:     eric.dumazet@...il.com, gnault@...hat.com
Subject: [PATCH net v3] 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 in l2tp_recv_common.

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 v3:
1. To keep consistency, move the code out of l2tp_recv_common.
2. Use "net" instead of "net-next", since this is a bug fix.

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 |  4 ++++
 net/l2tp/l2tp_core.h | 21 +++++++++++++++++++++
 net/l2tp/l2tp_ip.c   |  3 +++
 net/l2tp/l2tp_ip6.c  |  3 +++
 4 files changed, 31 insertions(+)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 26f1d435696a..82c28008b438 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -884,6 +884,10 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb)
 		goto error;
 	}
 
+	if (tunnel->version != L2TP_HDR_VER_2 &&
+	    l2tp_v3_pull_opt(session, skb, &ptr, &optr))
+		goto error;
+
 	l2tp_recv_common(session, skb, ptr, optr, hdrflags, length);
 	l2tp_session_dec_refcount(session);
 
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 9c9afe94d389..870f8ccf95f7 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -301,6 +301,27 @@ static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
 }
 #endif
 
+/* Pull optional fields of L2TPv3 */
+static inline int l2tp_v3_pull_opt(struct l2tp_session *session, struct sk_buff *skb,
+				   unsigned char **ptr, unsigned char **optr)
+{
+	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))
+			return -1;
+
+		if (skb->data != *optr) {
+			*optr = skb->data;
+			*ptr = skb->data + off;
+		}
+	}
+
+	return 0;
+}
+
 #define l2tp_printk(ptr, type, func, fmt, ...)				\
 do {									\
 	if (((ptr)->debug) & (type))					\
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 35f6f86d4dcc..adc736d0a553 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -165,6 +165,9 @@ static int l2tp_ip_recv(struct sk_buff *skb)
 		print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
 	}
 
+	if (l2tp_v3_pull_opt(session, skb, &ptr, &optr))
+		goto discard_sess;
+
 	l2tp_recv_common(session, skb, ptr, optr, 0, skb->len);
 	l2tp_session_dec_refcount(session);
 
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index 237f1a4a0b0c..a023bb6eae03 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -178,6 +178,9 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
 		print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
 	}
 
+	if (l2tp_v3_pull_opt(session, skb, &ptr, &optr))
+		goto discard_sess;
+
 	l2tp_recv_common(session, skb, ptr, optr, 0, skb->len);
 	l2tp_session_dec_refcount(session);
 
-- 
2.17.1