diff options
Diffstat (limited to '')
| -rw-r--r-- | net/ipv4/inet_hashtables.c | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 45fb450b4522..c96866a53a66 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -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); |