2021-05-31 20:32:15

by Johannes Berg

[permalink] [raw]
Subject: [PATCH v4.9 02/10] mac80211: prevent mixed key and fragment cache attacks

From: Mathy Vanhoef <[email protected]>

commit 94034c40ab4a3fcf581fbc7f8fdf4e29943c4a24 upstream.

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: [email protected]
Signed-off-by: Mathy Vanhoef <[email protected]>
Link: https://lore.kernel.org/r/202105[email protected]changeid
Signed-off-by: Johannes Berg <[email protected]>
---
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 9c20c53f6729..5bca7994b58c 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 6e02f8dfce2b..4e23f240f599 100644
--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -647,6 +647,7 @@ int ieee80211_key_link(struct ieee80211_key *key,
struct sta_info *sta)
{
struct ieee80211_local *local = sdata->local;
+ 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;
@@ -658,6 +659,12 @@ int ieee80211_key_link(struct ieee80211_key *key,
bool delay_tailroom = sdata->vif.type == NL80211_IFTYPE_STATION;
int ret;

+ /*
+ * 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);
+
mutex_lock(&sdata->local->key_mtx);

if (sta && pairwise)
diff --git a/net/mac80211/key.h b/net/mac80211/key.h
index 4aa20cef0859..2749a7d05e76 100644
--- a/net/mac80211/key.h
+++ b/net/mac80211/key.h
@@ -127,6 +127,8 @@ 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 e5760492c27d..d3aee2859f0a 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2004,6 +2004,7 @@ 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);
@@ -2041,6 +2042,11 @@ 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]++;
--
2.31.1