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    Subject[PATCH 5.4 06/51] ipv6: use siphash in rt6_exception_hash()
    Date
    From: Eric Dumazet <edumazet@google.com>

    commit 4785305c05b25a242e5314cc821f54ade4c18810 upstream.

    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@google.com>
    Reported-by: Keyu Man <kman001@ucr.edu>
    Cc: Wei Wang <weiwan@google.com>
    Cc: Martin KaFai Lau <kafai@fb.com>
    Acked-by: Wei Wang <weiwan@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [OP: adjusted context for 5.4 stable]
    Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/route.c | 20 ++++++++++++++------
    1 file changed, 14 insertions(+), 6 deletions(-)

    --- 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>
    @@ -1502,17 +1503,24 @@ static void rt6_exception_remove_oldest(
    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 = jhash(dst, sizeof(*dst), seed);
    + net_get_random_once(&rt6_exception_key, sizeof(rt6_exception_key));

    #ifdef CONFIG_IPV6_SUBTREES
    if (src)
    - val = jhash(src, sizeof(*src), 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

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