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l2tp: copy 4 more bytes to linear part if necessary 

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: fd558d186d ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Suggested-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
Acked-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jacob Wen 2019-01-31 15:18:56 +08:00 committed by David S. Miller
parent 3aa9179b2d
commit 91c524708d
1 changed files with 2 additions and 3 deletions
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5
net/l2tp/l2tp_core.c
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@ -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 */
#define L2TP_DEFAULT_DEBUG_FLAGS 0
@ -808,7 +807,7 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb)
__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);