[PATCH 4.19 03/32] inet: switch IP ID generator to siphash

Greg Kroah-Hartman
2019-06-03T09:09:50Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit df453700e8d81b1bdafdf684365ee2b9431fb702 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/siphash.h | 5 +++++
include/net/netns/ipv4.h | 2 ++
net/ipv4/route.c | 12 +++++++-----
net/ipv6/output_core.c | 30 ++++++++++++++++--------------
4 files changed, 30 insertions(+), 19 deletions(-)

--- 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);
--- 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;
@@ -214,5 +215,6 @@ struct netns_ipv4 {
unsigned int ipmr_seq; /* protected by rtnl_mutex */

atomic_t rt_genid;
+ siphash_key_t ip_id_key;
};
#endif
--- 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);
}
--- 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 ne
*/
__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 ne
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);