[PATCH 3.18 049/104] netns: provide pure entropy for net_hash_mix()

Greg Kroah-Hartman
2019-04-24T18:12:23Z

From: Eric Dumazet <edumazet@google.com>

[ 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>
---
include/net/net_namespace.h | 2 ++
include/net/netns/hash.h | 15 ++-------------
net/core/net_namespace.c | 1 +
3 files changed, 5 insertions(+), 13 deletions(-)

--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -54,6 +54,8 @@ struct net {
#endif
spinlock_t rules_mod_lock;

+ u32 hash_mix;
+
struct list_head list; /* list of network namespaces */
struct list_head cleanup_list; /* namespaces on death row */
struct list_head exit_list; /* Use only net_mutex */
--- a/include/net/netns/hash.h
+++ b/include/net/netns/hash.h
@@ -1,21 +1,10 @@
#ifndef __NET_NS_HASH_H__
#define __NET_NS_HASH_H__

-#include <asm/cache.h>
-
-struct net;
+#include <net/net_namespace.h>

static inline unsigned int net_hash_mix(struct net *net)
{
-#ifdef CONFIG_NET_NS
- /*
- * shift this right to eliminate bits, that are
- * always zeroed
- */
-
- return (unsigned)(((unsigned long)net) >> L1_CACHE_SHIFT);
-#else
- return 0;
-#endif
+ return net->hash_mix;
}
#endif
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -156,6 +156,7 @@ static __net_init int setup_net(struct n

atomic_set(&net->count, 1);
atomic_set(&net->passive, 1);
+ get_random_bytes(&net->hash_mix, sizeof(u32));
net->dev_base_seq = 1;
net->user_ns = user_ns;