netdev - Re: possible deadlock in cfg80211_netdev_notifier

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Date:   Mon, 01 Feb 2021 13:49:18 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Mike Rapoport <rppt@...ux.ibm.com>,
        syzbot <syzbot+2ae0ca9d7737ad1a62b7@...kaller.appspotmail.com>
Cc:     akpm@...ux-foundation.org, davem@...emloft.net, hagen@...u.net,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        sfr@...b.auug.org.au, syzkaller-bugs@...glegroups.com
Subject: Re: possible deadlock in cfg80211_netdev_notifier_call

On Mon, 2021-02-01 at 14:37 +0200, Mike Rapoport wrote:
> On Mon, Feb 01, 2021 at 01:17:13AM -0800, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    b01f250d Add linux-next specific files for 20210129
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14daa408d00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=725bc96dc234fda7
> > dashboard link: https://syzkaller.appspot.com/bug?extid=2ae0ca9d7737ad1a62b7
> > compiler:       gcc (GCC) 10.1.0-syz 20200507
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1757f2a0d00000
> > 
> > The issue was bisected to:
> > 
> > commit cc9327f3b085ba5be5639a5ec3ce5b08a0f14a7c
> > Author: Mike Rapoport <rppt@...ux.ibm.com>
> > Date:   Thu Jan 28 07:42:40 2021 +0000
> > 
> >     mm: introduce memfd_secret system call to create "secret" memory areas
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1505d28cd00000
> > final oops:     https://syzkaller.appspot.com/x/report.txt?x=1705d28cd00000
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1305d28cd00000
> 
> Sounds really weird to me. At this point the memfd_secret syscall is not
> even wired to arch syscall handlers. I cannot see how it can be a reason of
> deadlock in wireless...

Yeah, forget about it. Usually this is a consequence of the way syzbot
creates tests - it might have created something like

  if (!create_secret_memfd())
    return;
  try_something_on_wireless()

and then of course without your patch it cannot get to the wireless
bits.

Pretty sure I know what's going on here, I'll take a closer look later.

johannes