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>

diff --git a/include/linux/siphash.h b/include/linux/siphash.h
index fa7a6b9cedbffeac141a157790115288132f43e9..bf21591a9e5e653585c26cb3f3f0857256c0eb89 100644 (file)
--- a/include/linux/siphash.h
+++ b/include/linux/siphash.h
@@ -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);

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 104a6669e3445c1ac43fee5fba9060c565005b62..7698460a3dd1e5070e12d406b3ee58834688cdc9 100644 (file)
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -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

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 14c7fdacaa72ed2180169c3befb2aa04ce1e3093..f2688fce39e1262cb3b615933502739b369859f7 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -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);
 }

diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index 4fe7c90962ddae3356200376aa911bab6d75bb48..868ae23dbae195de0e81fcad2566af2420294d7e 100644 (file)
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -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);