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Message-ID: <CA+55aFyTFzML+_8E_kDjX=YFkaDi_ejGo15UgGtAT29244UwgA@mail.gmail.com>
Date: Fri, 21 Apr 2017 10:42:48 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andrey Konovalov <andreyknvl@...gle.com>,
Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Alexey Kuznetsov <kuznet@....inr.ac.ru>,
James Morris <jmorris@...ei.org>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
Patrick McHardy <kaber@...sh.net>,
netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Alexander Duyck <alexander.h.duyck@...el.com>,
David Ahern <dsa@...ulusnetworks.com>,
Daniel Borkmann <daniel@...earbox.net>,
tcharding <me@...in.cc>, Jiri Pirko <jiri@...lanox.com>,
stephen hemminger <stephen@...workplumber.org>,
Dmitry Vyukov <dvyukov@...gle.com>,
Kostya Serebryany <kcc@...gle.com>,
syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/core: BUG in unregister_netdevice_many
On Fri, Apr 21, 2017 at 10:25 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'm assuming that the real cause is simply that "dev->reg_state" ends
> up being NETREG_UNREGISTERING or something. Maybe the BUG_ON() could
> be just removed, and replaced by the previous warning about
> NETREG_UNINITIALIZED.
>
> Something like the attached (TOTALLY UNTESTED) patch.
.. might as well test it.
That patch doesn't fix the problem, but it does show that yes, it was
NETREG_UNREGISTERING:
unregister_netdevice: device pim6reg/ffff962dc4606000 was not registered (2)
but then immediately afterwards we get
general protection fault: 0000 [#1] SMP
Workqueue: netns cleanup_net
RIP: 0010:dev_shutdown+0xe/0xc0
Call Trace:
rollback_registered_many+0x2a5/0x440
unregister_netdevice_many+0x1e/0xb0
default_device_exit_batch+0x145/0x170
which is due to a
mov 0x388(%rdi),%eax
where %rdi is 0xdead000000000090. That is at the very beginning of
dev_shutdown, it's "dev" itself that has that value, so it comes from
(_another_) invocation of rollback_registered_many(), when it does
that
list_for_each_entry(dev, head, unreg_list) {
so it seems to be a case of another "list_del() leaves list in bad
state", and it was the added test for "dev->reg_state !=
NETREG_REGISTERED" that did that
list_del(&dev->unreg_list);
and left random contents in the unreg_list.
So that "handle error case" was almost certainly just buggy too.
And the bug seems to be that we're trying to unregister a netdevice
that has already been unregistered.
Over to Eric and networking people. This oops is user-triggerable, and
leaves the machine in a bad state (the original BUG_ON() and the new
GP fault both happen while holding the RTNL, so networking is not
healthy afterwards.
Linus
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