netdev - Re: [PATCH] net: mac80211: cfg: enforce sanity checks for key_index in ieee80211_del

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Date:   Tue, 01 Dec 2020 13:06:01 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Anant Thazhemadam <anant.thazhemadam@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+49d4cab497c2142ee170@...kaller.appspotmail.com
Subject: Re: [PATCH] net: mac80211: cfg: enforce sanity checks for key_index
 in ieee80211_del_key()

On Tue, 2020-12-01 at 17:26 +0530, Anant Thazhemadam wrote:
> On 01/12/20 3:30 pm, Johannes Berg wrote:
> > On Tue, 2020-12-01 at 15:26 +0530, Anant Thazhemadam wrote:
> > > Currently, it is assumed that key_idx values that are passed to
> > > ieee80211_del_key() are all valid indexes as is, and no sanity checks
> > > are performed for it.
> > > However, syzbot was able to trigger an array-index-out-of-bounds bug
> > > by passing a key_idx value of 5, when the maximum permissible index
> > > value is (NUM_DEFAULT_KEYS - 1).
> > > Enforcing sanity checks helps in preventing this bug, or a similar
> > > instance in the context of ieee80211_del_key() from occurring.
> > I think we should do this more generally in cfg80211, like in
> > nl80211_new_key() we do it via cfg80211_validate_key_settings().
> > 
> > I suppose we cannot use the same function, but still, would be good to
> > address this generally in nl80211 for all drivers.
> 
> Hello,
> 
> This gave me the idea of trying to use cfg80211_validate_key_settings()
> directly in ieee80211_del_key(). I did try that out, tested it, and this bug
> doesn't seem to be getting triggered anymore.
> If this is okay, then I can send in a v2 soon. :)
> 
> If there is any reason that I'm missing as to why cfg80211_validate_key_settings()
> cannot be used in this context, please let me know.

If it works then I guess that's OK. I thought we didn't have all the
right information, e.g. whether a key is pairwise or not?

johannes