linux-kernel - Re: [PATCH v2] wifi: cfg80211: Fix UAF in ieee80211_scan

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Message-ID: <182980137c6.5665bf61226802.3084448395277966678@siddh.me>
Date:   Sat, 13 Aug 2022 21:49:52 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     "Jakub Kicinski" <kuba@...nel.org>
Cc:     "greg kh" <gregkh@...uxfoundation.org>,
        "johannes berg" <johannes@...solutions.net>,
        "david s. miller" <davem@...emloft.net>,
        "eric dumazet" <edumazet@...gle.com>,
        "paolo abeni" <pabeni@...hat.com>,
        "netdev" <netdev@...r.kernel.org>,
        "syzbot+6cb476b7c69916a0caca" 
        <syzbot+6cb476b7c69916a0caca@...kaller.appspotmail.com>,
        "linux-wireless" <linux-wireless@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "syzbot+f9acff9bf08a845f225d" 
        <syzbot+f9acff9bf08a845f225d@...kaller.appspotmail.com>,
        "syzbot+9250865a55539d384347" 
        <syzbot+9250865a55539d384347@...kaller.appspotmail.com>,
        "linux-kernel-mentees" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [PATCH v2] wifi: cfg80211: Fix UAF in ieee80211_scan_rx()

On Sat, 13 Aug 2022 00:55:09 +0530  Jakub Kicinski  wrote:
> Similarly to Greg, I'm not very familiar with the code base but one
> sure way to move things forward would be to point out a commit which
> broke things and put it in a Fixes tag. Much easier to validate a fix
> by looking at where things went wrong.

Thanks, I now looked at some history.

The following commit on 28 Sep 2020 put the kfree call before NULLing:
c8cb5b854b40 ("nl80211/cfg80211: support 6 GHz scanning")

The following commit on 19 Nov 2014 introduces RCU:
6ea0a69ca21b ("mac80211: rcu-ify scan and scheduled scan request pointers")

The kfree call wasn't "rcu-ified" in this commit, and neither were
RCU heads added.

The following commit on 18 Dec 2014 added RCU head for sched_scan_req:
31a60ed1e95a ("nl80211: Convert sched_scan_req pointer to RCU pointer")

It seems a similar thing might not have been done for scan_req, but I
could have also missed commits.

So what should go into the fixes tag, if any? Probably 6ea0a69ca21b?

Also, I probably should use RCU_INIT_POINTER in this patch. Or should
I make a patch somewhat like 31a60ed1e95a?

Thanks,
Siddh