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sae: Reject group changes

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SAE protocol is meant to authenticate peers simultaneously.  Hence it
includes a tie-breaker provision in case both peers enter into the
Committed state and the Commit messages arrive at the respective peers
near simultaneously.

However, in the case of STA or Infrastructure mode, only one peer (STA)
would normally enter the Committed state (via Init) and the tie-breaker
provision is not needed.  If this condition is detected, abort the
connection.

Also remove the uneeded group change check in process_commit.
This commit is contained in:
Denis Kenzior 2021-07-09 23:35:37 -05:00
parent 7d67192493
commit 18ec5589f8
1 changed files with 3 additions and 69 deletions
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72
src/sae.c
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@ -485,7 +485,6 @@ static int sae_process_commit(struct sae_sm *sm, const uint8_t *from,
uint8_t kck_and_pmk[2][32];
uint8_t tmp[L_ECC_SCALAR_MAX_BYTES];
struct l_ecc_scalar *tmp_scalar;
uint16_t group;
uint16_t reason = MMPDU_REASON_CODE_UNSPECIFIED;
ssize_t klen;
struct l_ecc_scalar *order;
@ -502,15 +501,8 @@ static int sae_process_commit(struct sae_sm *sm, const uint8_t *from,
goto reject;
}
group = l_get_le16(ptr);
ptr += 2;
if (group != sm->group) {
sae_reject_authentication(sm,
MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP);
return 0;
}
sm->p_scalar = l_ecc_scalar_new(sm->curve, ptr, nbytes);
if (!sm->p_scalar) {
l_error("Server sent invalid P_Scalar during commit");
@ -863,69 +855,11 @@ static int sae_verify_committed(struct sae_sm *sm, uint16_t transaction,
if (len < 2)
return -EBADMSG;
if (l_get_le16(frame) == sm->group)
return 0;
if (!l_ecc_curve_from_ike_group(l_get_le16(frame))) {
if (sm->sync > SAE_SYNC_MAX)
return -EBADMSG;
sm->sync++;
goto reject_unsupp_group;
if (l_get_le16(frame) != sm->group) {
l_error("SAE: Peer tried to change group -- Reject");
return -EPROTO;
}
/*
* If we get here we know that the groups do not match, but the
* group provided in the frame is supported. From section
* 12.4.8.6.4 we see:
*
* "If the group is supported but does not match that used when
* the protocol instance constructed its SAE Commit message,
* DiffGrp shall be set and the local identity and peer identity
* shall be checked"
*/
if (memcmp(sm->handshake->spa, sm->handshake->aa, 6) > 0) {
/*
* "The mesh STA, with the numerically greater of the two
* MAC addresses, drops the received SAE Commit message,
* retransmits its last SAE Commit message, and shall
* set the t0 (retransmission) timer and remain in
* Committed state"
*/
sae_send_commit(sm, true);
return 0;
}
/*
* "The mesh STA, with the numerically lesser of the two
* MAC addresses, zeros Sync, shall increment Sc, choose
* the group from the received SAE Commit message,
* generate new PWE and new secret values according to
* 12.4.5.2, process the received SAE Commit message
* according to 12.4.5.4, generate a new SAE Commit
* message and SAE Confirm message, and shall transmit
* the new Commit and Confirm to the peer. It shall then
* transition to Confirmed state."
*/
sm->sync = 0;
sm->sc++;
sm->group = l_get_le16(frame);
sm->curve = l_ecc_curve_from_ike_group(sm->group);
sae_send_commit(sm, false);
sm->state = SAE_STATE_CONFIRMED;
/*
* The processing and sending of the confirm message
* will happen after we return. Since we have set the
* state to CONFIRMED, our confirm handler will get
* called.
*/
return 0;
default:
/*