[PATCH net-next] ipv6: switch inet6_addr_hash() to less predictable hash

[PATCH net-next] ipv6: switch inet6_addr_hash() to less predictable hash

[Eric Dumazet]

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@google.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

Re: [PATCH net-next] ipv6: switch inet6_addr_hash() to less predictable hash

[David Ahern]

On 10/8/24 6:01 AM, Eric Dumazet wrote:
> 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@google.com>
> ---
>  net/ipv6/addrconf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>

Re: [PATCH net-next] ipv6: switch inet6_addr_hash() to less predictable hash

[Kuniyuki Iwashima]

From: Eric Dumazet <edumazet@google.com>
Date: Tue,  8 Oct 2024 12:01:01 +0000
> 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@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Re: [PATCH net-next] ipv6: switch inet6_addr_hash() to less predictable hash

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue,  8 Oct 2024 12:01:01 +0000 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net-next] ipv6: switch inet6_addr_hash() to less predictable hash
    https://git.kernel.org/netdev/net-next/c/4a0ec2aa0704

You are awesome, thank you!
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