From: Jouni Malinen <j@xxxxx> [ Upstream commit 6f601265215a421f425ba3a4850a35861d024643 ] TKIP replay protection was skipped for the very first frame received after a new key is configured. While this is potentially needed to avoid dropping a frame in some cases, this does leave a window for replay attacks with group-addressed frames at the station side. Any earlier frame sent by the AP using the same key would be accepted as a valid frame and the internal RSC would then be updated to the TSC from that frame. This would allow multiple previously transmitted group-addressed frames to be replayed until the next valid new group-addressed frame from the AP is received by the station. Fix this by limiting the no-replay-protection exception to apply only for the case where TSC=0, i.e., when this is for the very first frame protected using the new key, and the local RSC had not been set to a higher value when configuring the key (which may happen with GTK). Signed-off-by: Jouni Malinen <j@xxxxx> Link: https://lore.kernel.org/r/20200107153545.10934-1-j@xxxxx Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- net/mac80211/tkip.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/net/mac80211/tkip.c b/net/mac80211/tkip.c index 727dc9f3f3b3a..e7f57bb18f6e0 100644 --- a/net/mac80211/tkip.c +++ b/net/mac80211/tkip.c @@ -263,9 +263,21 @@ int ieee80211_tkip_decrypt_data(struct arc4_ctx *ctx, if ((keyid >> 6) != key->conf.keyidx) return TKIP_DECRYPT_INVALID_KEYIDX; - if (rx_ctx->ctx.state != TKIP_STATE_NOT_INIT && - (iv32 < rx_ctx->iv32 || - (iv32 == rx_ctx->iv32 && iv16 <= rx_ctx->iv16))) + /* Reject replays if the received TSC is smaller than or equal to the + * last received value in a valid message, but with an exception for + * the case where a new key has been set and no valid frame using that + * key has yet received and the local RSC was initialized to 0. This + * exception allows the very first frame sent by the transmitter to be + * accepted even if that transmitter were to use TSC 0 (IEEE 802.11 + * described TSC to be initialized to 1 whenever a new key is taken into + * use). + */ + if (iv32 < rx_ctx->iv32 || + (iv32 == rx_ctx->iv32 && + (iv16 < rx_ctx->iv16 || + (iv16 == rx_ctx->iv16 && + (rx_ctx->iv32 || rx_ctx->iv16 || + rx_ctx->ctx.state != TKIP_STATE_NOT_INIT))))) return TKIP_DECRYPT_REPLAY; if (only_iv) { -- 2.20.1
