[PATCH] mac80211: fix rx->key NULL dereference during mic failure

[PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Arik Nemtsov]

Sometimes when reporting a MIC failure rx->key may be unset. This
code path is hit when receiving a packet meant for a multicast
address, and decryption is performed in HW.

Fortunately, the failing key_idx is not used for anything up to
(and including) usermode, so we allow ourselves to set a bogus one
when a key cannot be retrieved.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
---
 net/mac80211/wpa.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/mac80211/wpa.c b/net/mac80211/wpa.c
index 9dc3b5f..c6dafc1 100644
--- a/net/mac80211/wpa.c
+++ b/net/mac80211/wpa.c
@@ -154,7 +154,8 @@ update_iv:
 	return RX_CONTINUE;
 
 mic_fail:
-	mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
+	mac80211_ev_michael_mic_failure(rx->sdata,
+					rx->key ? rx->key->conf.keyidx : -1,
 					(void *) skb->data, NULL, GFP_ATOMIC);
 	return RX_DROP_UNUSABLE;
 }
-- 
1.7.4.1

Re: [PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Johannes Berg]

On Sat, 2011-06-18 at 21:45 +0300, Arik Nemtsov wrote:
> Sometimes when reporting a MIC failure rx->key may be unset. This
> code path is hit when receiving a packet meant for a multicast
> address, and decryption is performed in HW.
> 
> Fortunately, the failing key_idx is not used for anything up to
> (and including) usermode, so we allow ourselves to set a bogus one
> when a key cannot be retrieved.

I guess we don't have a choice, but for the record I don't really like
lying. I'd rather also adjust nl80211 to not have the attribute in this
case, rather than an attribute with a bogus value.

johannes

Re: [PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Kalle Valo]

Arik Nemtsov <arik@wizery.com> writes:

> Sometimes when reporting a MIC failure rx->key may be unset. This
> code path is hit when receiving a packet meant for a multicast
> address, and decryption is performed in HW.
>
> Fortunately, the failing key_idx is not used for anything up to
> (and including) usermode, so we allow ourselves to set a bogus one
> when a key cannot be retrieved.

[...]

> -	mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
> +	mac80211_ev_michael_mic_failure(rx->sdata,
> +					rx->key ? rx->key->conf.keyidx : -1,
>  					(void *) skb->data, NULL, GFP_ATOMIC);

In special cases like this a comment in the code would be nice.

-- 
Kalle Valo

Re: [PATCH] mac80211: fix rx->key NULL dereference during mic failure

[John W. Linville]

On Sun, Jun 19, 2011 at 11:04:12PM +0300, Kalle Valo wrote:
> Arik Nemtsov <arik@wizery.com> writes:
> 
> > Sometimes when reporting a MIC failure rx->key may be unset. This
> > code path is hit when receiving a packet meant for a multicast
> > address, and decryption is performed in HW.
> >
> > Fortunately, the failing key_idx is not used for anything up to
> > (and including) usermode, so we allow ourselves to set a bogus one
> > when a key cannot be retrieved.
> 
> [...]
> 
> > -	mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
> > +	mac80211_ev_michael_mic_failure(rx->sdata,
> > +					rx->key ? rx->key->conf.keyidx : -1,
> >  					(void *) skb->data, NULL, GFP_ATOMIC);
> 
> In special cases like this a comment in the code would be nice.

Repost with a comment, as Kalle requested?

-- 
John W. Linville		Someday the world will need a hero, and you
linville@tuxdriver.com			might be all we have.  Be ready.

Re: [PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Arik Nemtsov]

> >
> > > -   mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
> > > +   mac80211_ev_michael_mic_failure(rx->sdata,
> > > +                                   rx->key ? rx->key->conf.keyidx : -1,
> > >                                     (void *) skb->data, NULL, GFP_ATOMIC);
> >
> > In special cases like this a comment in the code would be nice.
>
> Repost with a comment, as Kalle requested?
>

Sure thing.

Arik

Re: [PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Arik Nemtsov]

On Wed, Jun 22, 2011 at 23:52, Johannes Berg <johannes@sipsolutions.net> wrote:
> On Wed, 2011-06-22 at 23:41 +0300, Arik Nemtsov wrote:
>> Sometimes when reporting a MIC failure rx->key may be unset. This
>> code path is hit when receiving a packet meant for a multicast
>> address, and decryption is performed in HW.
>>
>> Fortunately, the failing key_idx is not used for anything up to
>> (and including) usermode, so we allow ourselves to drop it on the
>> way up when a key cannot be retrieved.
>>
>> Signed-off-by: Arik Nemtsov <arik@wizery.com>
>
> It'd be nice to also update the docs for the cfg80211 function to
> document the -1 special case, but other than that:

Sure why not? :)

Re: [PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Johannes Berg]

On Wed, 2011-06-22 at 23:41 +0300, Arik Nemtsov wrote:
> Sometimes when reporting a MIC failure rx->key may be unset. This
> code path is hit when receiving a packet meant for a multicast
> address, and decryption is performed in HW.
> 
> Fortunately, the failing key_idx is not used for anything up to
> (and including) usermode, so we allow ourselves to drop it on the
> way up when a key cannot be retrieved.
> 
> Signed-off-by: Arik Nemtsov <arik@wizery.com>

It'd be nice to also update the docs for the cfg80211 function to
document the -1 special case, but other than that:

Reviewed-by: Johannes Berg <johannes@sipsolutions.net>

johannes

[PATCH] mac80211: fix rx->key NULL dereference during mic failure

[Arik Nemtsov]

Sometimes when reporting a MIC failure rx->key may be unset. This
code path is hit when receiving a packet meant for a multicast
address, and decryption is performed in HW.

Fortunately, the failing key_idx is not used for anything up to
(and including) usermode, so we allow ourselves to drop it on the
way up when a key cannot be retrieved.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
---
We now discard invalid key indices on the way up, as Johannes
suggested privately.

net/mac80211/wpa.c     |    8 +++++++-
 net/wireless/nl80211.c |    3 ++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/wpa.c b/net/mac80211/wpa.c
index 9dc3b5f..d91c1a2 100644
--- a/net/mac80211/wpa.c
+++ b/net/mac80211/wpa.c
@@ -154,7 +154,13 @@ update_iv:
 	return RX_CONTINUE;
 
 mic_fail:
-	mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
+	/*
+	 * In some cases the key can be unset - e.g. a multicast packet, in
+	 * a driver that supports HW encryption. Send up the key idx only if
+	 * the key is set.
+	 */
+	mac80211_ev_michael_mic_failure(rx->sdata,
+					rx->key ? rx->key->conf.keyidx : -1,
 					(void *) skb->data, NULL, GFP_ATOMIC);
 	return RX_DROP_UNUSABLE;
 }
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index ec83f41..785549d 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -6464,7 +6464,8 @@ void nl80211_michael_mic_failure(struct cfg80211_registered_device *rdev,
 	if (addr)
 		NLA_PUT(msg, NL80211_ATTR_MAC, ETH_ALEN, addr);
 	NLA_PUT_U32(msg, NL80211_ATTR_KEY_TYPE, key_type);
-	NLA_PUT_U8(msg, NL80211_ATTR_KEY_IDX, key_id);
+	if (key_id != -1)
+		NLA_PUT_U8(msg, NL80211_ATTR_KEY_IDX, key_id);
 	if (tsc)
 		NLA_PUT(msg, NL80211_ATTR_KEY_SEQ, 6, tsc);
 
-- 
1.7.4.1