Commit 6f601265 authored Jan 07, 2020 by Jouni Malinen Committed by Johannes Berg Jan 15, 2020

mac80211: Fix TKIP replay protection immediately after key setup

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@w1.fi>
Link: https://lore.kernel.org/r/20200107153545.10934-1-j@w1.fi

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

parent 26ec17a1

net/mac80211/tkip.c

+15 −3

Original line number	Diff line number	Diff line
		@@ -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) {

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