netns: provide pure entropy for net_hash_mix()

BugLink: https://bugs.launchpad.net/bugs/1838116
[ Upstream commit 355b98553789b646ed97ad801a619ff898471b92 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 06cba8e1541f77bf02248935d1f811cc0208fa57..ce5bbe6f002ea7ef379bf771aa928ef156258ac7 100644 (file)
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -57,6 +57,7 @@ struct net {
                                                 */
        spinlock_t              rules_mod_lock;
 
+       u32                     hash_mix;
        atomic64_t              cookie_gen;
 
        struct list_head        list;           /* list of network namespaces */

diff --git a/include/net/netns/hash.h b/include/net/netns/hash.h
index 24c78183a4c262e086c29cde1e61b7f397d8bab0..d9b665151f3d9e916f35620141542a5a145e6123 100644 (file)
--- a/include/net/netns/hash.h
+++ b/include/net/netns/hash.h
@@ -2,21 +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
-       /*
-        * shift this right to eliminate bits, that are
-        * always zeroed
-        */
-
-       return (u32)(((unsigned long)net) >> L1_CACHE_SHIFT);
-#else
-       return 0;
-#endif
+       return net->hash_mix;
 }
 #endif

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 9b826d3b20e3c0f3d0fbe7a80eb298e300b2f551..b4e864012473131fd27183c019d2fc1b1b39bad8 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -287,6 +287,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 
        atomic_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);