netdev - [RFC PATCH ipsec] xfrm: don't pass too short packets to userspace with ESPINUDP encap

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Message-Id: <18a669995a73fefd70e179e6bc11b74e397e56ad.1595594449.git.sd@queasysnail.net>
Date:   Fri, 24 Jul 2020 16:46:07 +0200
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     netdev@...r.kernel.org
Cc:     Sabrina Dubroca <sd@...asysnail.net>,
        Paul Wouters <paul@...ats.ca>,
        Andrew Cagney <andrew.cagney@...il.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Tobias Brunner <tobias@...ongswan.org>
Subject: [RFC PATCH ipsec] xfrm: don't pass too short packets to userspace with ESPINUDP encap

Currently, any UDP-encapsulated packet of 8 bytes or less will be
passed to userspace, whether it starts with the non-ESP prefix or
not (except keepalives). This includes:
 - messages of 1, 2, 3 bytes
 - messages of 4 to 8 bytes not starting with 00 00 00 00

This patch changes that behavior, so that only properly-formed non-ESP
messages are passed to userspace. Messages of 8 bytes or less that
don't contain a full non-ESP prefix followed by some data (at least
one byte) will be dropped and counted as XfrmInHdrError.

Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
---
 net/ipv4/xfrm4_input.c | 9 +++++++--
 net/ipv6/xfrm6_input.c | 9 +++++++--
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/xfrm4_input.c b/net/ipv4/xfrm4_input.c
index ad2afeef4f10..2a2bb38ac798 100644
--- a/net/ipv4/xfrm4_input.c
+++ b/net/ipv4/xfrm4_input.c
@@ -114,9 +114,14 @@ int xfrm4_udp_encap_rcv(struct sock *sk, struct sk_buff *skb)
 		} else if (len > sizeof(struct ip_esp_hdr) && udpdata32[0] != 0) {
 			/* ESP Packet without Non-ESP header */
 			len = sizeof(struct udphdr);
-		} else
-			/* Must be an IKE packet.. pass it through */
+		} else if (len > 4 && udpdata32[0] == 0) {
+			/* IKE packet: pass it through */
 			return 1;
+		} else {
+			/* incomplete packet, drop */
+			XFRM_INC_STATS(dev_net(skb->dev), LINUX_MIB_XFRMINHDRERROR);
+			goto drop;
+		}
 		break;
 	case UDP_ENCAP_ESPINUDP_NON_IKE:
 		/* Check if this is a keepalive packet.  If so, eat it. */
diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c
index 04cbeefd8982..7e14d59d55cb 100644
--- a/net/ipv6/xfrm6_input.c
+++ b/net/ipv6/xfrm6_input.c
@@ -110,9 +110,14 @@ int xfrm6_udp_encap_rcv(struct sock *sk, struct sk_buff *skb)
 		} else if (len > sizeof(struct ip_esp_hdr) && udpdata32[0] != 0) {
 			/* ESP Packet without Non-ESP header */
 			len = sizeof(struct udphdr);
-		} else
-			/* Must be an IKE packet.. pass it through */
+		} else if (len > 4 && udpdata32[0] == 0) {
+			/* IKE packet: pass it through */
 			return 1;
+		} else {
+			/* incomplete packet, drop */
+			XFRM_INC_STATS(dev_net(skb->dev), LINUX_MIB_XFRMINHDRERROR);
+			goto drop;
+		}
 		break;
 	case UDP_ENCAP_ESPINUDP_NON_IKE:
 		/* Check if this is a keepalive packet.  If so, eat it. */
-- 
2.27.0