Commit 4c2c8f03 authored by Willy Tarreau's avatar Willy Tarreau Committed by Jakub Kicinski

tcp: increase source port perturb table to 2^16

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: default avatarMoshe Kol <moshe.kol@mail.huji.ac.il>
Reported-by: default avatarYossi Gilad <yossi.gilad@mail.huji.ac.il>
Reported-by: default avatarAmit Klein <aksecurity@gmail.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarWilly Tarreau <w@1wt.eu>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent e9261476
......@@ -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;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment