netdev - Re: [PATCH net 1/2] ipv6: use siphash in rt6_exception

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Date:   Wed, 25 Aug 2021 17:11:48 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>, Willy Tarreau <w@....eu>,
        Keyu Man <kman001@....edu>, Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH net 1/2] ipv6: use siphash in rt6_exception_hash()

On Wed, Aug 25, 2021 at 4:17 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> A group of security researchers brought to our attention
> the weakness of hash function used in rt6_exception_hash()
>
> Lets use siphash instead of Jenkins Hash, to considerably
> reduce security risks.
>
> Following patch deals with IPv4.
>
> Fixes: 35732d01fe31 ("ipv6: introduce a hash table to store dst cache")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Keyu Man <kman001@....edu>
> Cc: Wei Wang <weiwan@...gle.com>
> Cc: Martin KaFai Lau <kafai@...com>
Acked-by: Wei Wang <weiwan@...gle.com>

Thanks Eric!

> ---
>
>
>
>  net/ipv6/route.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index b6ddf23d38330ded88509b8507998ce82a72799b..c5e8ecb96426bda619fe242351e40dcf6ff68bcf 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -41,6 +41,7 @@
>  #include <linux/nsproxy.h>
>  #include <linux/slab.h>
>  #include <linux/jhash.h>
> +#include <linux/siphash.h>
>  #include <net/net_namespace.h>
>  #include <net/snmp.h>
>  #include <net/ipv6.h>
> @@ -1484,17 +1485,24 @@ static void rt6_exception_remove_oldest(struct rt6_exception_bucket *bucket)
>  static u32 rt6_exception_hash(const struct in6_addr *dst,
>                               const struct in6_addr *src)
>  {
> -       static u32 seed __read_mostly;
> -       u32 val;
> +       static siphash_key_t rt6_exception_key __read_mostly;
> +       struct {
> +               struct in6_addr dst;
> +               struct in6_addr src;
> +       } __aligned(SIPHASH_ALIGNMENT) combined = {
> +               .dst = *dst,
> +       };
> +       u64 val;
>
> -       net_get_random_once(&seed, sizeof(seed));
> -       val = jhash2((const u32 *)dst, sizeof(*dst)/sizeof(u32), seed);
> +       net_get_random_once(&rt6_exception_key, sizeof(rt6_exception_key));
>
>  #ifdef CONFIG_IPV6_SUBTREES
>         if (src)
> -               val = jhash2((const u32 *)src, sizeof(*src)/sizeof(u32), val);
> +               combined.src = *src;
>  #endif
> -       return hash_32(val, FIB6_EXCEPTION_BUCKET_SIZE_SHIFT);
> +       val = siphash(&combined, sizeof(combined), &rt6_exception_key);
> +
> +       return hash_64(val, FIB6_EXCEPTION_BUCKET_SIZE_SHIFT);
>  }
>
>  /* Helper function to find the cached rt in the hash table
> --
> 2.33.0.rc2.250.ged5fa647cd-goog
>