linux-kernel - [PATCH v3 net 5/7] tcp: dynamically allocate the perturb table used by source ports

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Date:   Mon,  2 May 2022 10:46:12 +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>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, Willy Tarreau <w@....eu>
Subject: [PATCH v3 net 5/7] tcp: dynamically allocate the perturb table used by source ports

We'll need to further increase the size of this table and it's likely
that at some point its size will not be suitable anymore for a static
table. Let's allocate it on boot from inet_hashinfo2_init(), which is
called from tcp_init().

Cc: Moshe Kol <moshe.kol@...l.huji.ac.il>
Cc: Yossi Gilad <yossi.gilad@...l.huji.ac.il>
Cc: Amit Klein <aksecurity@...il.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 net/ipv4/inet_hashtables.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 63bb4902f018..48ca07853068 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -731,7 +731,8 @@ EXPORT_SYMBOL_GPL(inet_unhash);
  * privacy, this only consumes 1 KB of kernel memory.
  */
 #define INET_TABLE_PERTURB_SHIFT 8
-static u32 table_perturb[1 << INET_TABLE_PERTURB_SHIFT];
+#define INET_TABLE_PERTURB_SIZE (1 << INET_TABLE_PERTURB_SHIFT)
+static u32 *table_perturb;
 
 int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 		struct sock *sk, u64 port_offset,
@@ -774,7 +775,8 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 	if (likely(remaining > 1))
 		remaining &= ~1U;
 
-	net_get_random_once(table_perturb, sizeof(table_perturb));
+	net_get_random_once(table_perturb,
+			    INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb));
 	index = hash_32(port_offset, INET_TABLE_PERTURB_SHIFT);
 
 	offset = READ_ONCE(table_perturb[index]) + (port_offset >> 32);
@@ -912,6 +914,12 @@ void __init inet_hashinfo2_init(struct inet_hashinfo *h, const char *name,
 					    low_limit,
 					    high_limit);
 	init_hashinfo_lhash2(h);
+
+	/* this one is used for source ports of outgoing connections */
+	table_perturb = kmalloc_array(INET_TABLE_PERTURB_SIZE,
+				      sizeof(*table_perturb), GFP_KERNEL);
+	if (!table_perturb)
+		panic("TCP: failed to alloc table_perturb");
 }
 
 int inet_hashinfo2_init_mod(struct inet_hashinfo *h)
-- 
2.17.5