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Message-Id: <20220427065233.2075-8-w@1wt.eu>
Date: Wed, 27 Apr 2022 08:52:33 +0200
From: Willy Tarreau <w@....eu>
To: netdev@...r.kernel.org
Cc: David Miller <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Moshe Kol <moshe.kol@...l.huji.ac.il>,
Yossi Gilad <yossi.gilad@...l.huji.ac.il>,
Amit Klein <aksecurity@...il.com>,
linux-kernel@...r.kernel.org, Willy Tarreau <w@....eu>
Subject: [PATCH net 7/7] tcp: drop the hash_32() part from the index calculation
In commit 190cc82489f4 ("tcp: change source port randomizarion at
connect() time"), the table_perturb[] array was introduced and an
index was taken from the port_offset via hash_32(). But it turns
out that hash_32() performs a multiplication while the input here
comes from the output of SipHash in secure_seq, that is well
distributed enough to avoid the need for yet another hash.
Suggested-by: Amit Klein <aksecurity@...il.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
net/ipv4/inet_hashtables.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index f30c50aaf8e2..a75e66d7eee6 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -778,7 +778,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
net_get_random_once(table_perturb,
INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb));
- index = hash_32(port_offset, INET_TABLE_PERTURB_SHIFT);
+ index = port_offset & (INET_TABLE_PERTURB_SIZE - 1);
offset = (READ_ONCE(table_perturb[index]) + (port_offset >> 32)) % remaining;
/* In first pass we try ports of @low parity.
--
2.17.5
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