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netns: provide pure entropy for net_hash_mix()

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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: 0b4419162a ("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>
This commit is contained in:
Eric Dumazet 2019-03-27 08:21:30 -07:00 committed by David S. Miller
parent 6289d0facd
commit 355b985537
3 changed files with 4 additions and 8 deletions
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1
include/net/net_namespace.h
View File

@ -59,6 +59,7 @@ struct net {
*/
spinlock_t rules_mod_lock;
u32 hash_mix;
atomic64_t cookie_gen;
struct list_head list; /* list of network namespaces */

10
include/net/netns/hash.h
View File

@ -2,16 +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
return (u32)(((unsigned long)net) >> ilog2(sizeof(*net)));
#else
return 0;
#endif
return net->hash_mix;
}
#endif

1
net/core/net_namespace.c
View File

@ -304,6 +304,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
refcount_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);