netdev - [PATCH net 2/3] net: sched: ife: handle malformed tlv length

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Message-Id: <20180418213534.6215-3-aring@mojatatu.com>
Date:   Wed, 18 Apr 2018 17:35:33 -0400
From:   Alexander Aring <aring@...atatu.com>
To:     yotam.gi@...il.com
Cc:     jhs@...atatu.com, davem@...emloft.net, xiyou.wangcong@...il.com,
        jiri@...nulli.us, yuvalm@...lanox.com, netdev@...r.kernel.org,
        kernel@...atatu.com, Alexander Aring <aring@...atatu.com>
Subject: [PATCH net 2/3] net: sched: ife: handle malformed tlv length

There is currently no handling to check on a invalid tlv length. This
patch adds such handling to avoid killing the kernel with a malformed
ife packet.

Signed-off-by: Alexander Aring <aring@...atatu.com>
---
 include/net/ife.h   |  3 ++-
 net/ife/ife.c       | 35 +++++++++++++++++++++++++++++++++--
 net/sched/act_ife.c |  7 ++++++-
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/include/net/ife.h b/include/net/ife.h
index 44b9c00f7223..e117617e3c34 100644
--- a/include/net/ife.h
+++ b/include/net/ife.h
@@ -12,7 +12,8 @@
 void *ife_encode(struct sk_buff *skb, u16 metalen);
 void *ife_decode(struct sk_buff *skb, u16 *metalen);
 
-void *ife_tlv_meta_decode(void *skbdata, u16 *attrtype, u16 *dlen, u16 *totlen);
+void *ife_tlv_meta_decode(void *skbdata, const void *ifehdr_end, u16 *attrtype,
+			  u16 *dlen, u16 *totlen);
 int ife_tlv_meta_encode(void *skbdata, u16 attrtype, u16 dlen,
 			const void *dval);
 
diff --git a/net/ife/ife.c b/net/ife/ife.c
index 7d1ec76e7f43..8632d2685efb 100644
--- a/net/ife/ife.c
+++ b/net/ife/ife.c
@@ -92,12 +92,43 @@ struct meta_tlvhdr {
 	__be16 len;
 };
 
+static inline bool __ife_tlv_meta_valid(const unsigned char *skbdata,
+					const unsigned char *ifehdr_end)
+{
+	const struct meta_tlvhdr *tlv;
+	u16 tlvlen;
+
+	if (unlikely(skbdata + sizeof(*tlv) > ifehdr_end))
+		return false;
+
+	tlv = (struct meta_tlvhdr *)skbdata;
+	tlvlen = ntohs(tlv->len);
+
+	/* tlv length field is inc header, check on minimum */
+	if (tlvlen < NLA_HDRLEN)
+		return false;
+
+	/* overflow by NLA_ALIGN check */
+	if (NLA_ALIGN(tlvlen) < tlvlen)
+		return false;
+
+	if (unlikely(skbdata + NLA_ALIGN(tlvlen) > ifehdr_end))
+		return false;
+
+	return true;
+}
+
 /* Caller takes care of presenting data in network order
  */
-void *ife_tlv_meta_decode(void *skbdata, u16 *attrtype, u16 *dlen, u16 *totlen)
+void *ife_tlv_meta_decode(void *skbdata, const void *ifehdr_end, u16 *attrtype,
+			  u16 *dlen, u16 *totlen)
 {
-	struct meta_tlvhdr *tlv = (struct meta_tlvhdr *) skbdata;
+	struct meta_tlvhdr *tlv;
+
+	if (!__ife_tlv_meta_valid(skbdata, ifehdr_end))
+		return NULL;
 
+	tlv = (struct meta_tlvhdr *)skbdata;
 	*dlen = ntohs(tlv->len) - NLA_HDRLEN;
 	*attrtype = ntohs(tlv->type);
 
diff --git a/net/sched/act_ife.c b/net/sched/act_ife.c
index 49b8ab551fbe..8527cfdc446d 100644
--- a/net/sched/act_ife.c
+++ b/net/sched/act_ife.c
@@ -682,7 +682,12 @@ static int tcf_ife_decode(struct sk_buff *skb, const struct tc_action *a,
 		u16 mtype;
 		u16 dlen;
 
-		curr_data = ife_tlv_meta_decode(tlv_data, &mtype, &dlen, NULL);
+		curr_data = ife_tlv_meta_decode(tlv_data, ifehdr_end, &mtype,
+						&dlen, NULL);
+		if (!curr_data) {
+			qstats_drop_inc(this_cpu_ptr(ife->common.cpu_qstats));
+			return TC_ACT_SHOT;
+		}
 
 		if (find_decode_metaid(skb, ife, mtype, dlen, curr_data)) {
 			/* abuse overlimits to count when we receive metadata
-- 
2.11.0