netdev - [PATCH net-next] ipv6: switch inet6_addr

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Message-ID: <20241008120101.734521-1-edumazet@google.com>
Date: Tue,  8 Oct 2024 12:01:01 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: David Ahern <dsahern@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] ipv6: switch inet6_addr_hash() to less predictable hash

In commit 3f27fb23219e ("ipv6: addrconf: add per netns perturbation
in inet6_addr_hash()"), I added net_hash_mix() in inet6_addr_hash()
to get better hash dispersion, at a time all netns were sharing the
hash table.

Since then, commit 21a216a8fc63 ("ipv6/addrconf: allocate a per
netns hash table") made the hash table per netns.

We could remove the net_hash_mix() from inet6_addr_hash(), but
there is still an issue with ipv6_addr_hash().

It is highly predictable and a malicious user can easily create
thousands of IPv6 addresses all stored in the same hash bucket.

Switch to __ipv6_addr_jhash(). We could use a dedicated
secret, or reuse net_hash_mix() as I did in this patch.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/addrconf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 94dceac528842c47c18e71ad75e9d16ae373b4f2..f31528d4f694e42032276ddd6230b23911c480b5 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1016,7 +1016,7 @@ ipv6_link_dev_addr(struct inet6_dev *idev, struct inet6_ifaddr *ifp)

 static u32 inet6_addr_hash(const struct net *net, const struct in6_addr *addr)
 {
-	u32 val = ipv6_addr_hash(addr) ^ net_hash_mix(net);
+	u32 val = __ipv6_addr_jhash(addr, net_hash_mix(net));

 	return hash_32(val, IN6_ADDR_HSIZE_SHIFT);
 }
-- 
2.47.0.rc0.187.ge670bccf7e-goog