| From 7a8477db1947c3c4f3a2c3b1c30fe9ae3d2cdee6 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Mon, 2 May 2022 10:46:13 +0200 |
| Subject: tcp: increase source port perturb table to 2^16 |
| |
| From: Willy Tarreau <w@1wt.eu> |
| |
| [ Upstream commit 4c2c8f03a5ab7cb04ec64724d7d176d00bcc91e5 ] |
| |
| Moshe Kol, Amit Klein, and Yossi Gilad reported being able to accurately |
| identify a client by forcing it to emit only 40 times more connections |
| than there are entries in the table_perturb[] table. The previous two |
| improvements consisting in resalting the secret every 10s and adding |
| randomness to each port selection only slightly improved the situation, |
| and the current value of 2^8 was too small as it's not very difficult |
| to make a client emit 10k connections in less than 10 seconds. |
| |
| Thus we're increasing the perturb table from 2^8 to 2^16 so that the |
| same precision now requires 2.6M connections, which is more difficult in |
| this time frame and harder to hide as a background activity. The impact |
| is that the table now uses 256 kB instead of 1 kB, which could mostly |
| affect devices making frequent outgoing connections. However such |
| components usually target a small set of destinations (load balancers, |
| database clients, perf assessment tools), and in practice only a few |
| entries will be visited, like before. |
| |
| A live test at 1 million connections per second showed no performance |
| difference from the previous value. |
| |
| Reported-by: Moshe Kol <moshe.kol@mail.huji.ac.il> |
| Reported-by: Yossi Gilad <yossi.gilad@mail.huji.ac.il> |
| Reported-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: Sasha Levin <sashal@kernel.org> |
| --- |
| net/ipv4/inet_hashtables.c | 9 +++++---- |
| 1 file changed, 5 insertions(+), 4 deletions(-) |
| |
| diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c |
| index 763395e30c77..f76e4ac1ba3a 100644 |
| --- a/net/ipv4/inet_hashtables.c |
| +++ b/net/ipv4/inet_hashtables.c |
| @@ -726,11 +726,12 @@ EXPORT_SYMBOL_GPL(inet_unhash); |
| * Note that we use 32bit integers (vs RFC 'short integers') |
| * because 2^16 is not a multiple of num_ephemeral and this |
| * property might be used by clever attacker. |
| - * RFC claims using TABLE_LENGTH=10 buckets gives an improvement, |
| - * we use 256 instead to really give more isolation and |
| - * privacy, this only consumes 1 KB of kernel memory. |
| + * RFC claims using TABLE_LENGTH=10 buckets gives an improvement, though |
| + * attacks were since demonstrated, thus we use 65536 instead to really |
| + * give more isolation and privacy, at the expense of 256kB of kernel |
| + * memory. |
| */ |
| -#define INET_TABLE_PERTURB_SHIFT 8 |
| +#define INET_TABLE_PERTURB_SHIFT 16 |
| #define INET_TABLE_PERTURB_SIZE (1 << INET_TABLE_PERTURB_SHIFT) |
| static u32 *table_perturb; |
| |
| -- |
| 2.35.1 |
| |