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ipv6: use a stronger hash for tcp

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It looks like its possible to open thousands of TCP IPv6
sessions on a server, all landing in a single slot of TCP hash
table. Incoming packets have to lookup sockets in a very
long list.

We should hash all bits from foreign IPv6 addresses, using
a salt and hash mix, not a simple XOR.

inet6_ehashfn() can also separately use the ports, instead
of xoring them.

Reported-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2013-02-21 12:18:52 +00:00
committed by David S. Miller
parent 0ab8a9f5fa
commit 08dcdbf6a7
4 changed files with 24 additions and 6 deletions
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9
net/ipv4/af_inet.c
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@@ -248,8 +248,12 @@ EXPORT_SYMBOL(inet_listen);
u32 inet_ehash_secret __read_mostly;
EXPORT_SYMBOL(inet_ehash_secret);
u32 ipv6_hash_secret __read_mostly;
EXPORT_SYMBOL(ipv6_hash_secret);
/*
* inet_ehash_secret must be set exactly once
* inet_ehash_secret must be set exactly once, and to a non nul value
* ipv6_hash_secret must be set exactly once.
*/
void build_ehash_secret(void)
{
@@ -259,7 +263,8 @@ void build_ehash_secret(void)
get_random_bytes(&rnd, sizeof(rnd));
} while (rnd == 0);
cmpxchg(&inet_ehash_secret, 0, rnd);
if (cmpxchg(&inet_ehash_secret, 0, rnd) == 0)
get_random_bytes(&ipv6_hash_secret, sizeof(ipv6_hash_secret));
}
EXPORT_SYMBOL(build_ehash_secret);