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receiver: Use a time based limit to switch COOKIE secrets

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If we are under attack and there are lots of requests, we might hit
the previous use count limit pretty quickly and may switch secrets multiple
times a second, which renders the 10 second default lifetime of COOKIEs
pointless and prevents legitimate clients from sending requests with valid
COOKIEs.
This commit is contained in:
Tobias Brunner 2021-06-04 13:41:31 +02:00
parent 63260a11ca
commit 902fbd16e8
1 changed files with 32 additions and 32 deletions
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64
src/libcharon/network/receiver.c
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@ -33,8 +33,9 @@
#define COOKIE_LIFETIME 10
/** time we wait before disabling cookies */
#define COOKIE_CALMDOWN_DELAY 10
/** how many times to reuse the secret */
#define COOKIE_REUSE 10000
/** time in seconds we use a secret at most (since we keep two secrets, must
* be at least COOKIE_LIFETIME to process all outstanding valid cookies) */
#define COOKIE_SECRET_SWITCH 120
/** default value for private_receiver_t.cookie_threshold */
#define COOKIE_THRESHOLD_DEFAULT 10
/** default value for private_receiver_t.block_threshold */
@ -79,14 +80,9 @@ struct private_receiver_t {
char secret_old[SECRET_LENGTH];
/**
* how many times we have used "secret" so far
* time we used the current secret first
*/
uint32_t secret_used;
/**
* time we did the cookie switch
*/
uint32_t secret_switch;
uint32_t secret_first_use;
/**
* time offset to use, hides our system time
@ -232,7 +228,7 @@ static bool cookie_verify(private_receiver_t *this, message_t *message,
}
/* check if cookie is derived from old_secret */
if (t + this->secret_offset > this->secret_switch)
if (t + this->secret_offset >= this->secret_first_use)
{
secret = chunk_from_thing(this->secret);
}
@ -334,9 +330,33 @@ static bool drop_ike_sa_init(private_receiver_t *this, message_t *message)
{
chunk_t cookie;
DBG2(DBG_NET, "received packet from: %#H to %#H",
DBG2(DBG_NET, "received packet: from %#H to %#H (%zu bytes)",
message->get_source(message),
message->get_destination(message));
message->get_destination(message),
message->get_packet_data(message).len);
if (!this->secret_first_use)
{
this->secret_first_use = now;
}
else if (now - this->secret_first_use > COOKIE_SECRET_SWITCH)
{
char secret[SECRET_LENGTH];
DBG1(DBG_NET, "generating new cookie secret after %ds since first "
"use", now - this->secret_first_use);
if (this->rng->get_bytes(this->rng, SECRET_LENGTH, secret))
{
memcpy(this->secret_old, this->secret, SECRET_LENGTH);
memcpy(this->secret, secret, SECRET_LENGTH);
memwipe(secret, SECRET_LENGTH);
this->secret_first_use = now;
}
else
{
DBG1(DBG_NET, "failed to allocated cookie secret, keeping old");
}
}
if (!cookie_build(this, message, now - this->secret_offset,
chunk_from_thing(this->secret), &cookie))
{
@ -346,25 +366,6 @@ static bool drop_ike_sa_init(private_receiver_t *this, message_t *message)
message->get_source(message));
send_notify(message, IKEV2_MAJOR_VERSION, IKE_SA_INIT, COOKIE, cookie);
chunk_free(&cookie);
if (++this->secret_used > COOKIE_REUSE)
{
char secret[SECRET_LENGTH];
DBG1(DBG_NET, "generating new cookie secret after %d uses",
this->secret_used);
if (this->rng->get_bytes(this->rng, SECRET_LENGTH, secret))
{
memcpy(this->secret_old, this->secret, SECRET_LENGTH);
memcpy(this->secret, secret, SECRET_LENGTH);
memwipe(secret, SECRET_LENGTH);
this->secret_switch = now;
this->secret_used = 0;
}
else
{
DBG1(DBG_NET, "failed to allocated cookie secret, keeping old");
}
}
return TRUE;
}
@ -628,7 +629,6 @@ receiver_t *receiver_create()
.destroy = _destroy,
},
.esp_cb_mutex = mutex_create(MUTEX_TYPE_DEFAULT),
.secret_switch = now,
.secret_offset = now ? random() % now : 0,
);