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    Subject[PATCH 4.19 013/101] netns: provide pure entropy for net_hash_mix()
    Date
    [ 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: Sasha Levin <sashal@kernel.org>
    ---
    include/net/net_namespace.h | 1 +
    include/net/netns/hash.h | 10 ++--------
    net/core/net_namespace.c | 1 +
    3 files changed, 4 insertions(+), 8 deletions(-)

    diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
    index 9b5fdc50519a..3f7b166262d7 100644
    --- 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 16a842456189..d9b665151f3d 100644
    --- a/include/net/netns/hash.h
    +++ b/include/net/netns/hash.h
    @@ -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
    diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
    index 670c84b1bfc2..7320f0844a50 100644
    --- a/net/core/net_namespace.c
    +++ b/net/core/net_namespace.c
    @@ -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);
    --
    2.19.1


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