linux-kernel - Re: WARNING in hwsim_new_radio

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Date:   Tue, 14 Apr 2020 12:38:22 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     syzbot <syzbot+a4aee3f42d7584d76761@...kaller.appspotmail.com>,
        davem@...emloft.net, kvalo@...eaurora.org,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        mathew.j.martineau@...ux.intel.com, matthieu.baerts@...sares.net,
        netdev@...r.kernel.org, pabeni@...hat.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING in hwsim_new_radio_nl

Hi syzbot keepers,

On Mon, 2020-04-13 at 07:05 -0700, syzbot wrote:
> syzbot has bisected this bug to:
> 
> commit 01cacb00b35cb62b139f07d5f84bcf0eeda8eff6
> Author: Paolo Abeni <pabeni@...hat.com>
> Date:   Fri Mar 27 21:48:51 2020 +0000
> 
>     mptcp: add netlink-based PM
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10225bb3e00000

This is, fairly obviously, incorrect. Same with the bisection for
6693adf1698864d21734, which is really the same underlying problem as
this one (though at a different code site).

However, it stands out that this was bisected to a commit that adds a
new generic netlink family in both cases.

This makes sense - the reproducer identifies the family by *number*, but
that number isn't stable, generic netlink families should be identified
by *name*.

Perhaps somehow syzbot could be taught that, so that the bisection is
stable across kernels with different generic netlink families
registered?

Alternatively, we _could_ add some kind of stable ID mode, but I'm not
sure we really want to ... since that would mean people start hardcoding
IDs?

johannes