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Merge branch 'tcp-rfc-6056'

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Eric Dumazet says:

====================
tcp: RFC 6056 induced changes

This is based on a report from David Dworken.

First patch implements RFC 6056 3.3.4 proposal.

Second patch is adding a little bit of noise to make
attacker life a bit harder.
===================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2021-02-11 13:13:05 -08:00
commit 3a926b0e9c
1 changed files with 22 additions and 3 deletions
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25
net/ipv4/inet_hashtables.c
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@ -709,6 +709,17 @@ unlock:
}
EXPORT_SYMBOL_GPL(inet_unhash);
/* RFC 6056 3.3.4. Algorithm 4: Double-Hash Port Selection Algorithm
* 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.
*/
#define INET_TABLE_PERTURB_SHIFT 8
static u32 table_perturb[1 << INET_TABLE_PERTURB_SHIFT];
int __inet_hash_connect(struct inet_timewait_death_row *death_row,
struct sock *sk, u32 port_offset,
int (*check_established)(struct inet_timewait_death_row *,
@ -722,8 +733,8 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
struct inet_bind_bucket *tb;
u32 remaining, offset;
int ret, i, low, high;
static u32 hint;
int l3mdev;
u32 index;
if (port) {
head = &hinfo->bhash[inet_bhashfn(net, port,
@ -750,7 +761,10 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
if (likely(remaining > 1))
remaining &= ~1U;
offset = (hint + port_offset) % remaining;
net_get_random_once(table_perturb, sizeof(table_perturb));
index = hash_32(port_offset, INET_TABLE_PERTURB_SHIFT);
offset = (READ_ONCE(table_perturb[index]) + port_offset) % remaining;
/* In first pass we try ports of @low parity.
* inet_csk_get_port() does the opposite choice.
*/
@ -804,7 +818,12 @@ next_port:
return -EADDRNOTAVAIL;
ok:
hint += i + 2;
/* If our first attempt found a candidate, skip next candidate
* in 1/16 of cases to add some noise.
*/
if (!i && !(prandom_u32() % 16))
i = 2;
WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + 2);
/* Head lock still held and bh's disabled */
inet_bind_hash(sk, tb, port);