[PATCH 3.18 18/31] l2tp: copy 4 more bytes to linear part if necessary

From: Greg Kroah-Hartman
Date: Mon Feb 04 2019 - 05:38:25 EST

3.18-stable review patch. If anyone has any objections, please let me know.


From: Jacob Wen <jian.w.wen@xxxxxxxxxx>

[ Upstream commit 91c524708de6207f59dd3512518d8a1c7b434ee3 ]

The size of L2TPv2 header with all optional fields is 14 bytes.
l2tp_udp_recv_core only moves 10 bytes to the linear part of a
skb. This may lead to l2tp_recv_common read data outside of a skb.

This patch make sure that there is at least 14 bytes in the linear
part of a skb to meet the maximum need of l2tp_udp_recv_core and
l2tp_recv_common. The minimum size of both PPP HDLC-like frame and
Ethernet frame is larger than 14 bytes, so we are safe to do so.

Also remove L2TP_HDR_SIZE_NOSEQ, it is unused now.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Suggested-by: Guillaume Nault <gnault@xxxxxxxxxx>
Signed-off-by: Jacob Wen <jian.w.wen@xxxxxxxxxx>
Acked-by: Guillaume Nault <gnault@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/l2tp/l2tp_core.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -83,8 +83,7 @@
#define L2TP_SLFLAG_S 0x40000000
#define L2TP_SL_SEQ_MASK 0x00ffffff

-#define L2TP_HDR_SIZE_SEQ 10
-#define L2TP_HDR_SIZE_NOSEQ 6
+#define L2TP_HDR_SIZE_MAX 14

/* Default trace flags */
@@ -856,7 +855,7 @@ static int l2tp_udp_recv_core(struct l2t
__skb_pull(skb, sizeof(struct udphdr));

/* Short packet? */
- if (!pskb_may_pull(skb, L2TP_HDR_SIZE_SEQ)) {
+ if (!pskb_may_pull(skb, L2TP_HDR_SIZE_MAX)) {
l2tp_info(tunnel, L2TP_MSG_DATA,
"%s: recv short packet (len=%d)\n",
tunnel->name, skb->len);