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    SubjectRe: [PATCH 5.10 024/252] mac80211: prevent mixed key and fragment cache attacks
    Hi!

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

    > --- a/net/mac80211/key.c
    > +++ b/net/mac80211/key.c
    > @@ -799,6 +799,7 @@ int ieee80211_key_link(struct ieee80211_
    > struct ieee80211_sub_if_data *sdata,
    > struct sta_info *sta)
    > {
    > + static atomic_t key_color = ATOMIC_INIT(0);
    > struct ieee80211_key *old_key;

    This is nice and simple, but does not include any kind of overflow
    handling. sparc32 moved away from 24-bit atomics, which is good I
    guess. OTOH if this is incremented 10 times a second, we'll still
    overflow in 6 years or so. Can attacker make it overflow?

    Should this have a note why overflow is not possible / why it is not a
    problem?

    Best regards,
    Pavel

    --
    http://www.livejournal.com/~pavelmachek
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