[PATCH net-next] ipv6: switch inet6_acaddr_hash() to less predictable hash

[PATCH net-next] ipv6: switch inet6_acaddr_hash() to less predictable hash

[Eric Dumazet]

commit 2384d02520ff ("net/ipv6: Add anycast addresses to a global hashtable")
added inet6_acaddr_hash(), using ipv6_addr_hash() and net_hash_mix()
to get hash spreading for typical users.

However ipv6_addr_hash() is highly predictable and a malicious user
could abuse a specific 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/anycast.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/anycast.c b/net/ipv6/anycast.c
index 0627c4c18d1a5067a668da778ad444855194cbeb..562cace50ca9ae635dd0762e147b452be44c729c 100644
--- a/net/ipv6/anycast.c
+++ b/net/ipv6/anycast.c
@@ -49,9 +49,10 @@ static DEFINE_SPINLOCK(acaddr_hash_lock);
 
 static int ipv6_dev_ac_dec(struct net_device *dev, const struct in6_addr *addr);
 
-static u32 inet6_acaddr_hash(struct net *net, const struct in6_addr *addr)
+static u32 inet6_acaddr_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_acaddr_hash() to less predictable hash

[David Ahern]

On 10/8/24 6:13 AM, Eric Dumazet wrote:
> commit 2384d02520ff ("net/ipv6: Add anycast addresses to a global hashtable")
> added inet6_acaddr_hash(), using ipv6_addr_hash() and net_hash_mix()
> to get hash spreading for typical users.
> 
> However ipv6_addr_hash() is highly predictable and a malicious user
> could abuse a specific 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/anycast.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 

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

Re: [PATCH net-next] ipv6: switch inet6_acaddr_hash() to less predictable hash

[Kuniyuki Iwashima]

From: Eric Dumazet <edumazet@google.com>
Date: Tue,  8 Oct 2024 12:13:07 +0000
> commit 2384d02520ff ("net/ipv6: Add anycast addresses to a global hashtable")
> added inet6_acaddr_hash(), using ipv6_addr_hash() and net_hash_mix()
> to get hash spreading for typical users.
> 
> However ipv6_addr_hash() is highly predictable and a malicious user
> could abuse a specific 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_acaddr_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 12:13:07 +0000 you wrote:
> commit 2384d02520ff ("net/ipv6: Add anycast addresses to a global hashtable")
> added inet6_acaddr_hash(), using ipv6_addr_hash() and net_hash_mix()
> to get hash spreading for typical users.
> 
> However ipv6_addr_hash() is highly predictable and a malicious user
> could abuse a specific hash bucket.
> 
> [...]

Here is the summary with links:
  - [net-next] ipv6: switch inet6_acaddr_hash() to less predictable hash
    https://git.kernel.org/netdev/net-next/c/4daf4dc275f1

You are awesome, thank you!
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