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Subject[PATCH 3.16 155/157] inet: switch IP ID generator to siphash
3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

commit df453700e8d81b1bdafdf684365ee2b9431fb702 upstream.

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>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/include/linux/siphash.h
+++ b/include/linux/siphash.h
@@ -19,6 +19,11 @@ 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);
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -7,6 +7,7 @@

#include <linux/uidgid.h>
#include <net/inet_frag.h>
+#include <linux/siphash.h>

struct tcpm_hash_bucket;
struct ctl_table_header;
@@ -98,5 +99,6 @@ struct netns_ipv4 {
#endif
#endif
atomic_t rt_genid;
+ siphash_key_t ip_id_key;
};
#endif
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -486,15 +486,17 @@ 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);
}
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -9,14 +9,24 @@
#include <net/addrconf.h>
#include <net/secure_seq.h>

-static u32 __ipv6_select_ident(struct net *net, u32 hashrnd,
+static u32 __ipv6_select_ident(struct net *net,
struct in6_addr *dst, 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
@@ -39,7 +49,6 @@ static u32 __ipv6_select_ident(struct ne
*/
void 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;
@@ -51,11 +60,7 @@ void ipv6_proxy_select_ident(struct net
if (!addrs)
return;

- 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]);
skb_shinfo(skb)->ip6_frag_id = htonl(id);
}
EXPORT_SYMBOL_GPL(ipv6_proxy_select_ident);
@@ -63,13 +68,9 @@ EXPORT_SYMBOL_GPL(ipv6_proxy_select_iden
void ipv6_select_ident(struct net *net, struct frag_hdr *fhdr,
struct rt6_info *rt)
{
- 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, &rt->rt6i_dst.addr,
- &rt->rt6i_src.addr);
+ id = __ipv6_select_ident(net, &rt->rt6i_dst.addr, &rt->rt6i_src.addr);
fhdr->identification = htonl(id);
}
EXPORT_SYMBOL(ipv6_select_ident);
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