If an authentication frame of length <= 5 is sent sae will overflow an integer. The original cause of this was due to incorrectly using the sizeof(struct mmpdu_header). The header can be either 24 or 28 bytes depending on fc.order. sizeof does not account for this so 28 is always the calculated length. This, in addition to hostapd not including a group number when rejecting, cause this erroneous length calculation to be worked around as seen in the removed comment. The comment is still valid (and described again in another location) but the actual check for len == 4 is not correct. To fix this we now rely on mpdu_validate to check that the authentication frame is valid, and then take the difference from 'hdr' and 'auth' to find the true header length (either 24 or 28 bytes). Doing this lets us simply check if len < 6 and reject since this would not be a valid auth frame. --- src/sae.c | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-) -v2: * Added checks for cases where the length could be zero. This is only accepted in one case where the group number is missing from the rejection. All other cases should fail if len < 2. diff --git a/src/sae.c b/src/sae.c index 8f9425f1..a2e7cdd7 100644 --- a/src/sae.c +++ b/src/sae.c @@ -689,6 +689,9 @@ static int sae_verify_nothing(struct sae_sm *sm, uint16_t transaction, if (status != 0) return -EBADMSG; + if (len < 2) + return -EBADMSG; + /* reject with unsupported group */ if (l_get_le16(frame) != sm->group) { sae_reject_authentication(sm, @@ -909,6 +912,9 @@ static int sae_verify_confirmed(struct sae_sm *sm, uint16_t trans, if (sm->sync > SAE_SYNC_MAX) return -EBADMSG; + if (len < 2) + return -EBADMSG; + /* frame shall be silently discarded */ if (l_get_le16(frame) != sm->group) return 0; @@ -944,6 +950,9 @@ static bool sae_verify_accepted(struct sae_sm *sm, uint16_t trans, if (sm->sync > SAE_SYNC_MAX) return false; + if (len < 2) + return false; + sc = l_get_le16(frame); /* @@ -1021,25 +1030,13 @@ static int sae_rx_authenticate(struct auth_proto *ap, goto reject; } - len -= sizeof(struct mmpdu_header); + len -= ((const void *)auth - (const void *)hdr); - if (len < 4) { - l_error("bad packet length"); + if (len < 6) { + l_error("bad packet length %zu", len); goto reject; } - /* - * TODO: Hostapd seems to not include the group number when rejecting - * with an unsupported group, which violates the spec. This means our - * len == 4, but we can still recover this connection by renegotiating - * a new group. Because of this we need to special case this status - * code, as well as add the check in the verify function to allow for - * this missing group number. - */ - if (len == 4 && L_LE16_TO_CPU(auth->status) != - MMPDU_STATUS_CODE_UNSUPP_FINITE_CYCLIC_GROUP) - goto reject; - ret = sae_verify_packet(sm, L_LE16_TO_CPU(auth->transaction_sequence), L_LE16_TO_CPU(auth->status), auth->ies, len - 6); -- 2.17.1