This is a note to let you know that I've just added the patch titled netns: provide pure entropy for net_hash_mix() to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: netns-provide-pure-entropy-for-net_hash_mix.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Mon Apr 15 07:47:06 CEST 2019 From: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Wed, 27 Mar 2019 08:21:30 -0700 Subject: netns: provide pure entropy for net_hash_mix() From: Eric Dumazet <edumazet@xxxxxxxxxx> [ 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@xxxxxxxxxx> Reported-by: Amit Klein <aksecurity@xxxxxxxxx> Reported-by: Benny Pinkas <benny@xxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/net/net_namespace.h | 1 + include/net/netns/hash.h | 15 ++------------- net/core/net_namespace.c | 1 + 3 files changed, 4 insertions(+), 13 deletions(-) --- a/include/net/net_namespace.h +++ b/include/net/net_namespace.h @@ -53,6 +53,7 @@ struct net { */ spinlock_t rules_mod_lock; + u32 hash_mix; atomic64_t cookie_gen; struct list_head list; /* list of network namespaces */ --- 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 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 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -282,6 +282,7 @@ 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; idr_init(&net->netns_ids); Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are queue-4.9/netns-provide-pure-entropy-for-net_hash_mix.patch queue-4.9/tcp-ensure-dctcp-reacts-to-losses.patch