[PATCH 1/2] eap-tls: Drop cached session when phase2 fails

[PATCH 1/2] eap-tls: Drop cached session when phase2 fails

[Andrew Zaborowski]

If we have a TLS session cached from this attempt or a previous
successful connection attempt but the overall EAP method fails, forget
the session to improve the chances that authentication succeeds on the
next attempt considering that some authenticators strangely allow
resumption but can't handle it all the way to EAP method success.
Logically the session resumption in the TLS layers on the server should
be transparent to the EAP layers so I guess those may be failed
attempts to further optimise phase 2 when the server thinks it can
already trust the client.
---
 src/eap-tls-common.c | 52 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 47 insertions(+), 5 deletions(-)

diff --git a/src/eap-tls-common.c b/src/eap-tls-common.c
index 784a57ee..e21e215b 100644
--- a/src/eap-tls-common.c
+++ b/src/eap-tls-common.c
@@ -115,6 +115,7 @@ struct eap_tls_state {
 
 	bool expecting_frag_ack:1;
 	bool tunnel_ready:1;
+	bool tls_session_resumed:1;
 
 	struct l_queue *ca_cert;
 	struct l_certchain *client_cert;
@@ -129,8 +130,11 @@ static struct l_settings *eap_tls_session_cache;
 static eap_tls_session_cache_load_func_t eap_tls_session_cache_load;
 static eap_tls_session_cache_sync_func_t eap_tls_session_cache_sync;
 
-static void __eap_tls_common_state_reset(struct eap_tls_state *eap_tls)
+static void __eap_tls_common_state_reset(struct eap_state *eap)
 {
+	struct eap_tls_state *eap_tls = eap_get_data(eap);
+	const char *peer_id;
+
 	eap_tls->version_negotiated = EAP_TLS_VERSION_NOT_NEGOTIATED;
 	eap_tls->method_completed = false;
 	eap_tls->phase2_failed = false;
@@ -145,6 +149,41 @@ static void __eap_tls_common_state_reset(struct eap_tls_state *eap_tls)
 	if (eap_tls->tunnel)
 		l_tls_reset(eap_tls->tunnel);
 
+	/*
+	 * Drop the TLS session cache for this peer if the overall EAP
+	 * method didn't succeed.
+	 *
+	 * Additionally if the session was cached previously, meaning
+	 * that we've had a successful authentication at least once before,
+	 * and we now used session resumption successfully and the method
+	 * failed, become suspicious of this server's TLS session
+	 * resumption support.  Some authenticators strangely allow
+	 * resumption but can't handle it all the way to EAP method
+	 * success.  This improves the chances that authentication
+	 * succeeds on the next attempt.
+	 *
+	 * Drop the cache even if we have no indication that the
+	 * method failed but it just didn't succeed, to handle cases like
+	 * the server getting stuck and a timout occuring at a higher
+	 * layer.  The risk is that we may occasionally flush the session
+	 * data when there was only a momentary radio issue, invalid
+	 * phase2 credentials or decision to abort.  Those are not hot
+	 * paths.
+	 *
+	 * Note: TLS errors before the ready callback are handled in l_tls.
+	 */
+	peer_id = eap_get_peer_id(eap);
+	if (peer_id && eap_tls_session_cache && !eap_method_is_success(eap) &&
+			l_settings_has_group(eap_tls_session_cache, peer_id)) {
+		eap_tls_forget_peer(peer_id);
+
+		if (eap_tls->tls_session_resumed)
+			l_warn("EAP: method did not finish after successful TLS"
+				" session resumption.");
+	}
+
+	eap_tls->tls_session_resumed = false;
+
 	eap_tls->tx_frag_offset = 0;
 	eap_tls->tx_frag_last_len = 0;
 
@@ -187,7 +226,7 @@ bool eap_tls_common_state_reset(struct eap_state *eap)
 {
 	struct eap_tls_state *eap_tls = eap_get_data(eap);
 
-	__eap_tls_common_state_reset(eap_tls);
+	__eap_tls_common_state_reset(eap);
 
 	if (eap_tls->variant_ops->reset)
 		eap_tls->variant_ops->reset(eap_tls->variant_data);
@@ -199,7 +238,7 @@ void eap_tls_common_state_free(struct eap_state *eap)
 {
 	struct eap_tls_state *eap_tls = eap_get_data(eap);
 
-	__eap_tls_common_state_reset(eap_tls);
+	__eap_tls_common_state_reset(eap);
 
 	eap_set_data(eap, NULL);
 
@@ -244,7 +283,9 @@ static void eap_tls_tunnel_ready(const char *peer_identity, void *user_data)
 {
 	struct eap_state *eap = user_data;
 	struct eap_tls_state *eap_tls = eap_get_data(eap);
-	bool resumed = l_tls_get_session_resumed(eap_tls->tunnel);
+
+	eap_tls->tls_session_resumed =
+		l_tls_get_session_resumed(eap_tls->tunnel);
 
 	if (eap_tls->ca_cert && !peer_identity) {
 		l_error("%s: TLS did not verify AP identity",
@@ -265,7 +306,8 @@ static void eap_tls_tunnel_ready(const char *peer_identity, void *user_data)
 	if (!eap_tls->variant_ops->tunnel_ready)
 		return;
 
-	if (!eap_tls->variant_ops->tunnel_ready(eap, peer_identity, resumed))
+	if (!eap_tls->variant_ops->tunnel_ready(eap, peer_identity,
+						eap_tls->tls_session_resumed))
 		l_tls_close(eap_tls->tunnel);
 }
 
-- 
2.34.1

[PATCH 2/2] eap-tls: Add DisableEAPTLSCache bool setting

[Andrew Zaborowski]

Seeing that some authenticators can't handle TLS session caching
properly, allow the EAP-TLS-based methods session caching support to be
disabled per-network using a [Settings].DisableEAPTLSCache setting.
Defaults to false.

With the previous commit, authentication should succeed at least every
other attempt.  I'd also expect that EAP-TLS is not usually affected
because there's no phase2, unlike with EAP-PEAP/EAP-TTLS.
---
 src/eap-tls-common.c | 18 ++++++++++++++++--
 src/iwd.network.rst  | 10 ++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/eap-tls-common.c b/src/eap-tls-common.c
index e21e215b..b621d395 100644
--- a/src/eap-tls-common.c
+++ b/src/eap-tls-common.c
@@ -116,6 +116,7 @@ struct eap_tls_state {
 	bool expecting_frag_ack:1;
 	bool tunnel_ready:1;
 	bool tls_session_resumed:1;
+	bool tls_cache_disabled:1;
 
 	struct l_queue *ca_cert;
 	struct l_certchain *client_cert;
@@ -179,7 +180,8 @@ static void __eap_tls_common_state_reset(struct eap_state *eap)
 
 		if (eap_tls->tls_session_resumed)
 			l_warn("EAP: method did not finish after successful TLS"
-				" session resumption.");
+				" session resumption.  If this repeats consider"
+				" setting [Settings].DisableEAPTLSCache.");
 	}
 
 	eap_tls->tls_session_resumed = false;
@@ -691,7 +693,7 @@ static bool eap_tls_tunnel_init(struct eap_state *eap)
 	if (eap_tls->domain_mask)
 		l_tls_set_domain_mask(eap_tls->tunnel, eap_tls->domain_mask);
 
-	if (!eap_tls_session_cache_load)
+	if (!eap_tls_session_cache_load || eap_tls->tls_cache_disabled)
 		goto start;
 
 	if (!eap_tls_session_cache)
@@ -1040,6 +1042,13 @@ int eap_tls_common_settings_check(struct l_settings *settings,
 		return -EINVAL;
 	}
 
+	if (l_settings_has_key(settings, "Settings", "DisableEAPTLSCache") &&
+			!l_settings_get_bool(settings, "Settings",
+						"DisableEAPTLSCache", NULL)) {
+		l_error("Can't parse DisableEAPTLSCache");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -1051,6 +1060,7 @@ bool eap_tls_common_settings_load(struct eap_state *eap,
 	struct eap_tls_state *eap_tls;
 	char setting_key[72];
 	char *domain_mask_str;
+	bool bool_val;
 
 	L_AUTO_FREE_VAR(char *, value) = NULL;
 
@@ -1080,6 +1090,10 @@ bool eap_tls_common_settings_load(struct eap_state *eap,
 		l_free(domain_mask_str);
 	}
 
+	eap_tls->tls_cache_disabled =
+		l_settings_get_bool(settings, "Settings", "DisableEAPTLSCache",
+					&bool_val) && bool_val;
+
 	eap_set_data(eap, eap_tls);
 
 	return true;
diff --git a/src/iwd.network.rst b/src/iwd.network.rst
index d3692834..8833f33b 100644
--- a/src/iwd.network.rst
+++ b/src/iwd.network.rst
@@ -174,6 +174,16 @@ The group ``[Settings]`` contains general settings.
        Properly configured Access Points will typically update this setting
        appropriately via Transition Disable indications.  User customization
        of this value is thus typically not required.
+   * - DisableEAPTLSCache
+     - Values: true, **false**
+
+       Disables TLS session caching in EAP-TLS, EAP-TTLS and EAP-PEAP.
+       Some network authenticators may be misconfigured in a way that TLS
+       session resumption is allowed but actually attempting it will cause
+       the EAP method to fail or time out.  In that case, assuming the
+       credentials and other settings are correct, every other connection
+       attempt will fail as sessions are cached and forgotten in alternating
+       attempts.  Use this setting to disable caching for this network.
 
 Network Authentication Settings
 -------------------------------
-- 
2.34.1

Re: [PATCH 1/2] eap-tls: Drop cached session when phase2 fails

[Denis Kenzior]

Hi Andrew,

On 1/27/23 17:33, Andrew Zaborowski wrote:
> If we have a TLS session cached from this attempt or a previous
> successful connection attempt but the overall EAP method fails, forget
> the session to improve the chances that authentication succeeds on the
> next attempt considering that some authenticators strangely allow
> resumption but can't handle it all the way to EAP method success.
> Logically the session resumption in the TLS layers on the server should
> be transparent to the EAP layers so I guess those may be failed
> attempts to further optimise phase 2 when the server thinks it can
> already trust the client.
> ---
>   src/eap-tls-common.c | 52 +++++++++++++++++++++++++++++++++++++++-----
>   1 file changed, 47 insertions(+), 5 deletions(-)
> 

Applied, thanks.

Regards,
-Denis

Re: [PATCH 2/2] eap-tls: Add DisableEAPTLSCache bool setting

[Denis Kenzior]

Hi Andrew,

On 1/27/23 17:33, Andrew Zaborowski wrote:
> Seeing that some authenticators can't handle TLS session caching
> properly, allow the EAP-TLS-based methods session caching support to be
> disabled per-network using a [Settings].DisableEAPTLSCache setting.
> Defaults to false.
> 
> With the previous commit, authentication should succeed at least every
> other attempt.  I'd also expect that EAP-TLS is not usually affected
> because there's no phase2, unlike with EAP-PEAP/EAP-TTLS.
> ---
>   src/eap-tls-common.c | 18 ++++++++++++++++--
>   src/iwd.network.rst  | 10 ++++++++++
>   2 files changed, 26 insertions(+), 2 deletions(-)
> 

I modified this patch and commit description:
  - Renamed the setting to EAP-{TLS|TTLS|PEAP}FastReauthentication to be 
consistent with other EAP-TLS based method settings.
  - Moved the setting to [Security] instead of [Settings].  Again to be more 
consistent.
  - Modified the warning message to reflect the above.

Please double check that I didn't screw anything up.

Applied, thanks.

Regards,
-Denis