Commit a81a6b20 authored May 02, 2022 by Willy Tarreau Committed by Greg Kroah-Hartman Jun 25, 2022

tcp: drop the hash_32() part from the index calculation



commit e8161345ddbb66e449abde10d2fdce93f867eba9 upstream.

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@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 3c78eea6

net/ipv4/inet_hashtables.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -590,7 +590,7 @@ 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);
		offset %= remaining;