MIME-Version: 1.0
In-Reply-To: <20170618191854.17767-1-Jason@zx2c4.com>
References: <1497720871224217@kroah.com> <20170618191854.17767-1-Jason@zx2c4.com>
From: Emmanuel Grumbach <egrumbach@gmail.com>
Date: Sun, 18 Jun 2017 23:31:52 +0300
Message-ID: <CANUX_P1=8R5E8uk7VsqyAXQvRD52J1XdcL1R6R6GJeM_dv85vw@mail.gmail.com> (sfid-20170618_223208_904867_4E6579DD)
Subject: Re: [PATCH] mac80211/wpa: use constant time memory comparison for MACs
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Johannes Berg <johannes.berg@intel.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-wireless-owner@vger.kernel.org

On Sun, Jun 18, 2017 at 10:18 PM, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> Otherwise, we enable all sorts of forgeries via timing attack.

crypto_memneq's description says:

Returns 0 when data is equal, 1 otherwise.

Clearly this is not suitable here. You are allowing replay attacks...
For network drivers, this is worse than timing attacks. You still need
to explain how you can exploit timing attacks *on a remote system*. On
your local system, threads are impacted etc... Fine. On a remote
system (you are in Rx path here..) how do you exploit them?


>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> Cc: Johannes Berg <johannes@sipsolutions.net>
> Cc: linux-wireless@vger.kernel.org
> Cc: stable@vger.kernel.org
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> ---
> Here's the backport for 3.18.
>
>  net/mac80211/wpa.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/mac80211/wpa.c b/net/mac80211/wpa.c
> index 983527a4c1ab..49592c7e4199 100644
> --- a/net/mac80211/wpa.c
> +++ b/net/mac80211/wpa.c
> @@ -16,6 +16,7 @@
>  #include <asm/unaligned.h>
>  #include <net/mac80211.h>
>  #include <crypto/aes.h>
> +#include <crypto/algapi.h>
>
>  #include "ieee80211_i.h"
>  #include "michael.h"
> @@ -150,7 +151,7 @@ ieee80211_rx_h_michael_mic_verify(struct ieee80211_rx_data *rx)
>         data_len = skb->len - hdrlen - MICHAEL_MIC_LEN;
>         key = &rx->key->conf.key[NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY];
>         michael_mic(key, hdr, data, data_len, mic);
> -       if (memcmp(mic, data + data_len, MICHAEL_MIC_LEN) != 0)
> +       if (crypto_memneq(mic, data + data_len, MICHAEL_MIC_LEN) != 0)
>                 goto mic_fail;
>
>         /* remove Michael MIC from payload */
> @@ -520,7 +521,7 @@ ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
>
>         queue = rx->security_idx;
>
> -       if (memcmp(pn, key->u.ccmp.rx_pn[queue], IEEE80211_CCMP_PN_LEN) <= 0) {
> +       if (crypto_memneq(pn, key->u.ccmp.rx_pn[queue], IEEE80211_CCMP_PN_LEN) <= 0) {
>                 key->u.ccmp.replays++;
>                 return RX_DROP_UNUSABLE;
>         }
> @@ -771,7 +772,7 @@ ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
>                 bip_aad(skb, aad);
>                 ieee80211_aes_cmac(key->u.aes_cmac.tfm, aad,
>                                    skb->data + 24, skb->len - 24, mic);
> -               if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
> +               if (crypto_memneq(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
>                         key->u.aes_cmac.icverrors++;
>                         return RX_DROP_UNUSABLE;
>                 }
> --
> 2.13.1
>