[SRU Hirsute, Groovy, Focal/linux-oem-5.10, Focal/linux-oem-5.6, Focal 02/16] mac80211: prevent mixed key and fragment cache attacks

[Thadeu Lima de Souza Cascardo]

From: Mathy Vanhoef <Mathy.Vanhoef at kuleuven.be>

Simultaneously prevent mixed key attacks (CVE-2020-24587) and fragment
cache attacks (CVE-2020-24586). This is accomplished by assigning a
unique color to every key (per interface) and using this to track which
key was used to decrypt a fragment. When reassembling frames, it is
now checked whether all fragments were decrypted using the same key.

To assure that fragment cache attacks are also prevented, the ID that is
assigned to keys is unique even over (re)associations and (re)connects.
This means fragments separated by a (re)association or (re)connect will
not be reassembled. Because mac80211 now also prevents the reassembly of
mixed encrypted and plaintext fragments, all cache attacks are prevented.

Cc: stable at vger.kernel.org
Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef at kuleuven.be>
Link: https://lore.kernel.org/r/20210511200110.3f8290e59823.I622a67769ed39257327a362cfc09c812320eb979@changeid
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
(cherry picked from commit 94034c40ab4a3fcf581fbc7f8fdf4e29943c4a24)
CVE-2020-24586
CVE-2020-24587
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 net/mac80211/ieee80211_i.h | 1 +
 net/mac80211/key.c         | 7 +++++++
 net/mac80211/key.h         | 2 ++
 net/mac80211/rx.c          | 6 ++++++
 4 files changed, 16 insertions(+)

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 8e281c2e644d..9e2489935332 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -97,6 +97,7 @@ struct ieee80211_fragment_entry {
 	u8 rx_queue;
 	bool check_sequential_pn; /* needed for CCMP/GCMP */
 	u8 last_pn[6]; /* PN of the last fragment if CCMP was used */
+	unsigned int key_color;
 };
 
 
diff --git a/net/mac80211/key.c b/net/mac80211/key.c
index a4817aa4b171..56433ad45d4d 100644
--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -799,6 +799,7 @@ int ieee80211_key_link(struct ieee80211_key *key,
 		       struct ieee80211_sub_if_data *sdata,
 		       struct sta_info *sta)
 {
+	static atomic_t key_color = ATOMIC_INIT(0);
 	struct ieee80211_key *old_key;
 	int idx = key->conf.keyidx;
 	bool pairwise = key->conf.flags & IEEE80211_KEY_FLAG_PAIRWISE;
@@ -850,6 +851,12 @@ int ieee80211_key_link(struct ieee80211_key *key,
 	key->sdata = sdata;
 	key->sta = sta;
 
+	/*
+	 * Assign a unique ID to every key so we can easily prevent mixed
+	 * key and fragment cache attacks.
+	 */
+	key->color = atomic_inc_return(&key_color);
+
 	increment_tailroom_need_count(sdata);
 
 	ret = ieee80211_key_replace(sdata, sta, pairwise, old_key, key);
diff --git a/net/mac80211/key.h b/net/mac80211/key.h
index 7ad72e9b4991..1e326c89d721 100644
--- a/net/mac80211/key.h
+++ b/net/mac80211/key.h
@@ -128,6 +128,8 @@ struct ieee80211_key {
 	} debugfs;
 #endif
 
+	unsigned int color;
+
 	/*
 	 * key config, must be last because it contains key
 	 * material as variable length member
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index ec81c8484e6c..494ba6347cd0 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2254,6 +2254,7 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 			 * next fragment has a sequential PN value.
 			 */
 			entry->check_sequential_pn = true;
+			entry->key_color = rx->key->color;
 			memcpy(entry->last_pn,
 			       rx->key->u.ccmp.rx_pn[queue],
 			       IEEE80211_CCMP_PN_LEN);
@@ -2291,6 +2292,11 @@ ieee80211_rx_h_defragment(struct ieee80211_rx_data *rx)
 
 		if (!requires_sequential_pn(rx, fc))
 			return RX_DROP_UNUSABLE;
+
+		/* Prevent mixed key and fragment cache attacks */
+		if (entry->key_color != rx->key->color)
+			return RX_DROP_UNUSABLE;
+
 		memcpy(pn, entry->last_pn, IEEE80211_CCMP_PN_LEN);
 		for (i = IEEE80211_CCMP_PN_LEN - 1; i >= 0; i--) {
 			pn[i]++;
-- 
2.30.2