CVE-2019-10638 (published 2019-07-05T23:15Z)

In the Linux kernel before 5.1.7, a device can be tracked by an attacker using the IP ID values the kernel produces for connection-less protocols (e.g., UDP and ICMP). When such traffic is sent to multiple destination IP addresses, it is possible to obtain hash collisions (of indices to the counter array) and thereby obtain the hashing key (via enumeration). An attack may be conducted by hosting a crafted web page that uses WebRTC or gQUIC to force UDP traffic to attacker-controlled IP addresses.

Severity: MEDIUM
CVSS v2 base score: 4.3 (AV:N/AC:M/Au:N/C:P/I:N/A:N)
CVSS v3 base score: 6.5, MEDIUM (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N)

Weakness information:
cwe_id: CWE-326
cwe_name: Inadequate Encryption Strength
description: The product stores or transmits sensitive data using an encryption scheme that is theoretically sound, but is not strong enough for the level of protection required.
extended_description: A weak encryption scheme can be subjected to brute force attacks that have a reasonable chance of succeeding using current attack methods and resources.
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Eric Dumazet
author_date: 2019-03-27 12:40:33-07:00
msg: inet: switch IP ID generator to siphash

According to Amit Klein and Benny Pinkas, IP ID generation is too weak
and might be used by attackers.

Even with recent net_hash_mix() fix (netns: provide pure entropy for net_hash_mix())
having 64bit key and Jenkins hash is risky.

It is time to switch to siphash and its 128bit keys.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Reported-by: Benny Pinkas <benny@pinkas.net>
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: siphash.h
change_type: ModificationType.MODIFY
diff: @@ -21,6 +21,11 @@ typedef struct {
 	u64 key[2];
 } siphash_key_t;
 
+static inline bool siphash_key_is_zero(const siphash_key_t *key)
+{
+	return !(key->key[0] | key->key[1]);
+}
+
 u64 __siphash_aligned(const void *data, size_t len, const siphash_key_t *key);
 #ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 u64 __siphash_unaligned(const void *data, size_t len, const siphash_key_t *key);

programming_language: Shell
filename: ipv4.h
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,7 @@
 #include <linux/uidgid.h>
 #include <net/inet_frag.h>
 #include <linux/rcupdate.h>
+#include <linux/siphash.h>
 
 struct tcpm_hash_bucket;
 struct ctl_table_header;
@@ -217,5 +218,6 @@ struct netns_ipv4 {
 	unsigned int	ipmr_seq;	/* protected by rtnl_mutex */
 
 	atomic_t	rt_genid;
+	siphash_key_t	ip_id_key;
 };
 #endif

programming_language: C
filename: route.c
change_type: ModificationType.MODIFY
diff: @@ -500,15 +500,17 @@ EXPORT_SYMBOL(ip_idents_reserve);
 
 void __ip_select_ident(struct net *net, struct iphdr *iph, int segs)
 {
-	static u32 ip_idents_hashrnd __read_mostly;
 	u32 hash, id;
 
-	net_get_random_once(&ip_idents_hashrnd, sizeof(ip_idents_hashrnd));
+	/* Note the following code is not safe, but this is okay. */
+	if (unlikely(siphash_key_is_zero(&net->ipv4.ip_id_key)))
+		get_random_bytes(&net->ipv4.ip_id_key,
+				 sizeof(net->ipv4.ip_id_key));
 
-	hash = jhash_3words((__force u32)iph->daddr,
+	hash = siphash_3u32((__force u32)iph->daddr,
 			    (__force u32)iph->saddr,
-			    iph->protocol ^ net_hash_mix(net),
-			    ip_idents_hashrnd);
+			    iph->protocol,
+			    &net->ipv4.ip_id_key);
 	id = ip_idents_reserve(hash, segs);
 	iph->id = htons(id);
 }

programming_language: C
filename: output_core.c
change_type: ModificationType.MODIFY
diff: @@ -10,15 +10,25 @@
 #include <net/secure_seq.h>
 #include <linux/netfilter.h>
 
-static u32 __ipv6_select_ident(struct net *net, u32 hashrnd,
+static u32 __ipv6_select_ident(struct net *net,
 			       const struct in6_addr *dst,
 			       const struct in6_addr *src)
 {
+	const struct {
+		struct in6_addr dst;
+		struct in6_addr src;
+	} __aligned(SIPHASH_ALIGNMENT) combined = {
+		.dst = *dst,
+		.src = *src,
+	};
 	u32 hash, id;
 
-	hash = __ipv6_addr_jhash(dst, hashrnd);
-	hash = __ipv6_addr_jhash(src, hash);
-	hash ^= net_hash_mix(net);
+	/* Note the following code is not safe, but this is okay. */
+	if (unlikely(siphash_key_is_zero(&net->ipv4.ip_id_key)))
+		get_random_bytes(&net->ipv4.ip_id_key,
+				 sizeof(net->ipv4.ip_id_key));
+
+	hash = siphash(&combined, sizeof(combined), &net->ipv4.ip_id_key);
 
 	/* Treat id of 0 as unset and if we get 0 back from ip_idents_reserve,
 	 * set the hight order instead thus minimizing possible future
@@ -41,7 +51,6 @@ static u32 __ipv6_select_ident(struct net *net, u32 hashrnd,
  */
 __be32 ipv6_proxy_select_ident(struct net *net, struct sk_buff *skb)
 {
-	static u32 ip6_proxy_idents_hashrnd __read_mostly;
 	struct in6_addr buf[2];
 	struct in6_addr *addrs;
 	u32 id;
@@ -53,11 +62,7 @@ __be32 ipv6_proxy_select_ident(struct net *net, struct sk_buff *skb)
 	if (!addrs)
 		return 0;
 
-	net_get_random_once(&ip6_proxy_idents_hashrnd,
-			    sizeof(ip6_proxy_idents_hashrnd));
-
-	id = __ipv6_select_ident(net, ip6_proxy_idents_hashrnd,
-				 &addrs[1], &addrs[0]);
+	id = __ipv6_select_ident(net, &addrs[1], &addrs[0]);
 	return htonl(id);
 }
 EXPORT_SYMBOL_GPL(ipv6_proxy_select_ident);
@@ -66,12 +71,9 @@ __be32 ipv6_select_ident(struct net *net,
 			 const struct in6_addr *daddr,
 			 const struct in6_addr *saddr)
 {
-	static u32 ip6_idents_hashrnd __read_mostly;
 	u32 id;
 
-	net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd));
-
-	id = __ipv6_select_ident(net, ip6_idents_hashrnd, daddr, saddr);
+	id = __ipv6_select_ident(net, daddr, saddr);
 	return htonl(id);
 }
 EXPORT_SYMBOL(ipv6_select_ident);

programming_language: C
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Eric Dumazet
author_date: 2019-03-27 08:21:30-07:00
msg: netns: provide pure entropy for net_hash_mix()

net_hash_mix() currently uses kernel address of a struct net,
and is used in many places that could be used to reveal this
address to a patient attacker, thus defeating KASLR, for
the typical case (initial net namespace, &init_net is
not dynamically allocated)

I believe the original implementation tried to avoid spending
too many cycles in this function, but security comes first.

Also provide entropy regardless of CONFIG_NET_NS.

Fixes: 0b4419162aa6 ("netns: introduce the net_hash_mix "salt" for hashes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Reported-by: Benny Pinkas <benny@pinkas.net>
Cc: Pavel Emelyanov <xemul@openvz.org>
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: net_namespace.h
change_type: ModificationType.MODIFY
diff: @@ -59,6 +59,7 @@ struct net {
 						 */
 	spinlock_t		rules_mod_lock;
 
+	u32			hash_mix;
 	atomic64_t		cookie_gen;
 
 	struct list_head	list;		/* list of network namespaces */

programming_language: C
filename: hash.h
change_type: ModificationType.MODIFY
diff: @@ -2,16 +2,10 @@
 #ifndef __NET_NS_HASH_H__
 #define __NET_NS_HASH_H__
 
-#include <asm/cache.h>
-
-struct net;
+#include <net/net_namespace.h>
 
 static inline u32 net_hash_mix(const struct net *net)
 {
-#ifdef CONFIG_NET_NS
-	return (u32)(((unsigned long)net) >> ilog2(sizeof(*net)));
-#else
-	return 0;
-#endif
+	return net->hash_mix;
 }
 #endif

programming_language: C
filename: net_namespace.c
change_type: ModificationType.MODIFY
diff: @@ -304,6 +304,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 
 	refcount_set(&net->count, 1);
 	refcount_set(&net->passive, 1);
+	get_random_bytes(&net->hash_mix, sizeof(u32));
 	net->dev_base_seq = 1;
 	net->user_ns = user_ns;
 	idr_init(&net->netns_ids);

programming_language: C