CVE-2017-13715 (published 2017-08-29T01:35Z)

The __skb_flow_dissect function in net/core/flow_dissector.c in the Linux kernel before 4.3 does not ensure that n_proto, ip_proto, and thoff are initialized, which allows remote attackers to cause a denial of service (system crash) or possibly execute arbitrary code via a single crafted MPLS packet.

Severity: HIGH
CVSS v2 base score: 10.0 (AV:N/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3 base score: 9.8, CRITICAL (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-665
cwe_name: Improper Initialization
description: The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.
extended_description: This can have security implications when the associated resource is expected to have certain properties or values, such as a variable that determines whether a user has been authenticated or not.
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Tom Herbert
author_date: 2015-09-01 09:24:26-07:00
msg: flow_dissector: Jump to exit code in __skb_flow_dissect

Instead of returning immediately (on a parsing failure for instance) we
jump to cleanup code. This always sets protocol values in key_control
(even on a failure there is still valid information in the key_tags that
was set before the problem was hit).

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: flow_dissector.c
change_type: ModificationType.MODIFY
diff: @@ -130,6 +130,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 	struct flow_dissector_key_tags *key_tags;
 	struct flow_dissector_key_keyid *key_keyid;
 	u8 ip_proto = 0;
+	bool ret = false;
 
 	if (!data) {
 		data = skb->data;
@@ -171,7 +172,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 ip:
 		iph = __skb_header_pointer(skb, nhoff, sizeof(_iph), data, hlen, &_iph);
 		if (!iph || iph->ihl < 5)
-			return false;
+			goto out_bad;
 		nhoff += iph->ihl * 4;
 
 		ip_proto = iph->protocol;
@@ -197,7 +198,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 ipv6:
 		iph = __skb_header_pointer(skb, nhoff, sizeof(_iph), data, hlen, &_iph);
 		if (!iph)
-			return false;
+			goto out_bad;
 
 		ip_proto = iph->nexthdr;
 		nhoff += sizeof(struct ipv6hdr);
@@ -234,7 +235,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 
 		vlan = __skb_header_pointer(skb, nhoff, sizeof(_vlan), data, hlen, &_vlan);
 		if (!vlan)
-			return false;
+			goto out_bad;
 
 		if (skb_flow_dissector_uses_key(flow_dissector,
 						FLOW_DISSECTOR_KEY_VLANID)) {
@@ -256,7 +257,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		} *hdr, _hdr;
 		hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr);
 		if (!hdr)
-			return false;
+			goto out_bad;
 		proto = hdr->proto;
 		nhoff += PPPOE_SES_HLEN;
 		switch (proto) {
@@ -265,7 +266,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		case htons(PPP_IPV6):
 			goto ipv6;
 		default:
-			return false;
+			goto out_bad;
 		}
 	}
 	case htons(ETH_P_TIPC): {
@@ -275,9 +276,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		} *hdr, _hdr;
 		hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr);
 		if (!hdr)
-			return false;
-		key_basic->n_proto = proto;
-		key_control->thoff = (u16)nhoff;
+			goto out_bad;
 
 		if (skb_flow_dissector_uses_key(flow_dissector,
 						FLOW_DISSECTOR_KEY_TIPC_ADDRS)) {
@@ -287,7 +286,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 			key_addrs->tipcaddrs.srcnode = hdr->srcnode;
 			key_control->addr_type = FLOW_DISSECTOR_KEY_TIPC_ADDRS;
 		}
-		return true;
+		goto out_good;
 	}
 
 	case htons(ETH_P_MPLS_UC):
@@ -297,7 +296,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data,
 					   hlen, &_hdr);
 		if (!hdr)
-			return false;
+			goto out_bad;
 
 		if ((ntohl(hdr[0].entry) & MPLS_LS_LABEL_MASK) >>
 		     MPLS_LS_LABEL_SHIFT == MPLS_LABEL_ENTROPY) {
@@ -310,21 +309,17 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 					htonl(MPLS_LS_LABEL_MASK);
 			}
 
-			key_basic->n_proto = proto;
-			key_basic->ip_proto = ip_proto;
-			key_control->thoff = (u16)nhoff;
-
-			return true;
+			goto out_good;
 		}
 
-		return true;
+		goto out_good;
 	}
 
 	case htons(ETH_P_FCOE):
 		key_control->thoff = (u16)(nhoff + FCOE_HEADER_LEN);
 		/* fall through */
 	default:
-		return false;
+		goto out_bad;
 	}
 
 ip_proto_again:
@@ -337,7 +332,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 
 		hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data, hlen, &_hdr);
 		if (!hdr)
-			return false;
+			goto out_bad;
 		/*
 		 * Only look inside GRE if version zero and no
 		 * routing
@@ -357,7 +352,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 						     data, hlen, &_keyid);
 
 			if (!keyid)
-				return false;
+				goto out_bad;
 
 			if (skb_flow_dissector_uses_key(flow_dissector,
 							FLOW_DISSECTOR_KEY_GRE_KEYID)) {
@@ -378,7 +373,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 						   sizeof(_eth),
 						   data, hlen, &_eth);
 			if (!eth)
-				return false;
+				goto out_bad;
 			proto = eth->h_proto;
 			nhoff += sizeof(*eth);
 		}
@@ -395,7 +390,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		opthdr = __skb_header_pointer(skb, nhoff, sizeof(_opthdr),
 					      data, hlen, &_opthdr);
 		if (!opthdr)
-			return false;
+			goto out_bad;
 
 		ip_proto = opthdr[0];
 		nhoff += (opthdr[1] + 1) << 3;
@@ -415,10 +410,6 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		break;
 	}
 
-	key_basic->n_proto = proto;
-	key_basic->ip_proto = ip_proto;
-	key_control->thoff = (u16)nhoff;
-
 	if (skb_flow_dissector_uses_key(flow_dissector,
 					FLOW_DISSECTOR_KEY_PORTS)) {
 		key_ports = skb_flow_dissector_target(flow_dissector,
@@ -428,7 +419,15 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 							data, hlen);
 	}
 
-	return true;
+out_good:
+	ret = true;
+
+out_bad:
+	key_basic->n_proto = proto;
+	key_basic->ip_proto = ip_proto;
+	key_control->thoff = (u16)nhoff;
+
+	return ret;
 }
 EXPORT_SYMBOL(__skb_flow_dissect);
 

programming_language: C