Though TKIP is deprecated and insecure its trivial to support it in
AP mode as we already do in station. This is only to allow AP mode
for old hardware that may only support TKIP. If the hardware supports
any higher level cipher that will be chosen automatically.
The key descriptor version was hard coded to HMAC_SHA1_AES which
is correct when using IE_RSN_AKM_SUITE_PSK + CCMP. ap.c hard
codes the PSK AKM but still uses wiphy to select the cipher. In
theory there could be hardware that only supports TKIP which
would then make IWD non-compliant since a different key descriptor
version should be used with PSK + TKIP (HMAC_MD5_ARC4).
Now use a helper to sort out which key descriptor should be used
given the AKM and cipher suite.
About a month ago hostapd was changed to set the secure bit on
eapol frames during rekeys (bc36991791). The spec is ambiguous
about this and has conflicting info depending on the sections you
read (12.7.2 vs 12.7.6). According to the hostapd commit log TGme
is trying to clarify this and wants to set secure=1 in the case
of rekeys. Because of this, IWD is completely broken with rekeys
since its disallows secure=1 on PTK 1/4 and 2/4.
Now, a bool is passed to the verify functions which signifies if
the PTK has been negotiated already. If secure differs from this
the key frame is not verified.
After the initial handshake, once the TK has been installed, all frames
coming to the AP should be encrypted. However, it seems that some
kernel/driver combinations allow unencrypted EAPoL frames to be received
and forwarded to userspace. This can lead to various attacks.
Some drivers can report whether the EAPoL frame has been received
unencrypted. Use this information to drop unencrypted EAPoL frames
received after the initial handshake has been completed.
After the initial handshake, once the TK has been installed, all frames
coming from the AP should be encrypted. However, it seems that some
kernel/driver combinations allow unencrypted EAPoL frames to be received
and forwarded to userspace. This can lead to a denial-of-service attack
where receipt of an invalid, unencrypted EAP-Failure frame generated by
an adversary results in iwd terminating an ongoing connection.
Some drivers can report whether the EAPoL frame has been received
unencrypted. Use this information to drop unencrypted EAP frames
received after the initial handshake has been completed.
Reported-by: Domien Schepers <schepers.d@northeastern.edu>
After the initial handshake, once the TK has been installed, all frames
coming from the AP should be encrypted. However, it seems that some
kernel/driver combinations allow unencrypted EAPoL frames to be received
and forwarded to userspace. This can lead to a denial-of-service attack
where receipt of an invalid, unencrypted EAPoL 1/4 frame generated by an
adversary results in iwd terminating an ongoing connection.
Some drivers can report whether the EAPoL frame has been received
unencrypted. Use this information to drop unencrypted PTK 1/4 frames
received after the initial handshake has been completed.
Reported-by: Domien Schepers <schepers.d@northeastern.edu>
Do not fail an ongoing handshake when an invalid EAPoL frame is
received. Instead, follow the intent of 802.11-2020 section 12.7.2:
"EAPOL-Key frames containing invalid field values shall be silently
discarded."
This prevents a denial-of-service attack where receipt of an invalid,
unencrypted EAPoL 1/4 frame generated by an adversary results in iwd
terminating an ongoing connection.
Reported-by: Domien Schepers <schepers.d@northeastern.edu>
Since l_malloc is used the frame contents are not zero'ed automatically
which could result in random bytes being present in the frame which were
expected to be zero. This poses a problem when calculating the MIC as the
crypto operations are done on the entire frame with the expectation of
the MIC being zero.
Fixes: 83212f9b23 ("eapol: change eapol_create_common to support FILS")
oci variable is always set during handshake_util_find_kde. Do not
initialize it unnecessarily to help the compiler / static analysis find
potential issues.
If OCI is not used, then the oci array is never initialized. Do not try
to include it in our GTK 2_of_2 message.
Fixes: ad4d639854 ("eapol: include OCI in GTK 2/2")
802.11 added Extended Key IDs which aim to solve the issue of PTK
key replacement during rekeys. Since swapping out the existing PTK
may result in data loss because there may be in flight packets still
using the old PTK.
Extended Key IDs use two key IDs for the PTK, which toggle between
0 and 1. During a rekey a new PTK is derived which uses the key ID
not already taken by the existing PTK. This new PTK is added as RX
only, then message 4/4 is sent. This ensure message 4 is encrypted
using the previous PTK. Once sent, the new PTK can be modified to
both RX and TX and the rekey is complete.
To handle this in eapol the extended key ID KDE is parsed which
gives us the new PTK key index. Using the new handshake callback
(handshake_state_set_ext_tk) the new TK is installed. The 4th
message is also included as an argument which is taken care of by
netdev (in case waiting for NEW_KEY is required due to PAE socekts).
FT/FILS handle their own PMK derivation but rekeys still require
using the 4-way handshake. There is some ambiguity in the spec whether
or not the PMKID needs to be included in message 1/4 and it appears
that when rekeying after FT/FILS hostapd does not include a PMKID.
handshake_util_ap_ie_matches() is used to make sure that the RSN element
received from the Authenticator during handshake / association response
is the same as the one advertised in Beacon/Probe Response frames. This
utility tries to bitwise compare the element first, and only if that
fails, compares RSN members individually.
For FT, bitwise comparison will always fail since the PMKID has to be
included by the Authenticator in any RSN IEs included in Authenticate
& Association Response frames.
Perform the bitwise comparison as an optimization only during processing
of eapol message 3/4. Also keep the parsed rsn information for future
use and to possibly avoid re-parsing it during later checks.
Add a handshake event for use by the AP side for mechanisms that
allocate client IPs during the handshake: P2P address allocation and
FILS address assignment. This is emitted only when EAPOL or the
auth_proto is actually about to send the network configuration data to
the client so that ap.c can skip allocating a DHCP leases altogether if
the client doesn't send the required KDE or IE.
This returns the length of the actual contents, making the code a bit
easier to read and avoid the need to mask the KDE value which isn't
self-explanatory.
802.1x offloading needs a way to call SET_PMK after EAP finishes.
In the same manner as set_tk/gtk/igtk a new 'install_pmk' function
was added which eapol can call into after EAP completes.
Again the hs->support_ip_allocation flag is used for two purposes here,
first the user signals whether to support this mechanism through this
flag, then it reads the flag to find out if an IP was allocated.
Support IP allocation during the 4-Way Handshake as defined in the P2P
spec. This is the supplicant side implementation.
The API requires the user to set hs->support_ip_allocation true before
eapol_start(). On HANDSHAKE_EVENT_COMPLETE, if this same flag is still
set, we've received the IP lease, the netmask and the authenticator's
IP from the authenticator and there's no need to start DHCP. If the
flag is cleared, the user needs to use DHCP.
Reuse this flag on the authenticator side with a slightly different
meaning: when it's true we're forced to wait for the EAPoL-Start before
sending the first EAPoL-EAP frame to the supplicant, such as is required
in a WSC enrollee registration when the Association Request didn't have
a v2.0 WSC IE.
Handle EAPoL-EAP frames using our eap.c methods in authenticator mode
same as we do on the supplicant side. The user (ap.c) will only need to
set a valid 8021x_settings in the handshake object, same as on the
supplicant side.
On the supplicant side eapol_register would only register the eapol_sm
on a given netdev to start receiving frames and an eapol_start call is
required for the state machine to start executing. On the authenticator
side we shouldn't have the "early frame" problem but there's no reason
for the semantics of the two methods to be different. Somehow we were
doing everything in eapol_register and not using eapol_start if
hs->authenticator was true, so bring this in line with the supplicant
side and require eapol_start to be called also from ap.c.
Throughout the supplicant mode we'd use the eapol_sm_write wrapper but
in the authenticator mode we'd call __eapol_tx_packet directly. Adapt
eapol_sm_write to use the right destination address and use it
consistently.
sm->handshake already contains our RSN/WPA IE so there's no need to
rebuild it for msg 3/4, especially since we hardcode the fact that we
only support one pairwise cipher. If we start declaring more supported
ciphers and need to include a second RSNE we can first parse
sm->hs->authenticator_ie into a struct ir_rsn_info, overwrite the cipher
and rebuild it from that struct.
This way we duplicate less code and we hardcode fewer facts about the AP
in eapol.c which also helps in adding EAP-WSC.
In both FT or FILS EAPoL isn't used for the initial handshake and only
for the later re-keys. For FT we added the
eapol_sm_set_require_handshake mechanism to tell EAPoL to not require
the initial handshake and we can re-use it for FILS.
Currently an adversary can retransmit EAPOL Msg4/4 to make the AP
reinstall the PTK. Against older Linux kernels this can subsequently
be used to decrypt, replay, and possibly decrypt frames. See the
KRACK attacks research at krackattacks.com for attack scenarios.
In this case no machine-in-the-middle position is needed to trigger
the key reinstallation.
Fix this by using the ptk_complete boolean to track when the 4-way
handshake has completed (similar to its usage for clients). When
receiving a retransmitted Msg4/4 accept this frame but do not reinstall
the PTK.
Credits to Chris M. Stone, Sam Thomas, and Tom Chothia of Birmingham
University to help discover this issue.
James Prestwood