ipv6: make exception cache less predictible
Even after commit 4785305c ("ipv6: use siphash in rt6_exception_hash()"), an attacker can still use brute force to learn some secrets from a victim linux host. One way to defeat these attacks is to make the max depth of the hash table bucket a random value. Before this patch, each bucket of the hash table used to store exceptions could contain 6 items under attack. After the patch, each bucket would contains a random number of items, between 6 and 10. The attacker can no longer infer secrets. This is slightly increasing memory size used by the hash table, we do not expect this to be a problem. Following patch is dealing with the same issue in IPv4. Fixes: 35732d01 ("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> Reviewed-by: David Ahern <dsahern@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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