netdev - Re: [PATCH] net: tls: enable __GFP_ZERO upon tls

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Date: Fri, 30 Jun 2023 13:37:37 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Boris Pismenny <borisp@...dia.com>, 
	John Fastabend <john.fastabend@...il.com>, Jakub Kicinski <kuba@...nel.org>, herbert@...dor.apana.org.au, 
	linux-crypto@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	syzbot <syzbot+828dfc12440b4f6f305d@...kaller.appspotmail.com>, 
	Eric Biggers <ebiggers@...nel.org>, Aviad Yehezkel <aviadye@...dia.com>, 
	Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] net: tls: enable __GFP_ZERO upon tls_init()

On Fri, Jun 30, 2023 at 12:18 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Fri, 30 Jun 2023 at 12:11, Alexander Potapenko <glider@...gle.com> wrote:
> >
> > On Fri, Jun 30, 2023 at 12:02 PM Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > On Fri, 30 Jun 2023 at 11:53, Tetsuo Handa
> > > <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > > >
> > > > On 2023/06/30 18:36, Ard Biesheuvel wrote:
> > > > > Why are you sending this now?
> > > >
> > > > Just because this is currently top crasher and I can reproduce locally.
> > > >
> > > > > Do you have a reproducer for this issue?
> > > >
> > > > Yes. https://syzkaller.appspot.com/text?tag=ReproC&x=12931621900000 works.
> > > >
> > >
> > > Could you please share your kernel config and the resulting kernel log
> > > when running the reproducer? I'll try to reproduce locally as well,
> > > and see if I can figure out what is going on in the crypto layer
> >
> > The config together with the repro is available at
> > https://syzkaller.appspot.com/bug?extid=828dfc12440b4f6f305d, see the
> > latest row of the "Crashes" table that contains a C repro.
>
> Could you explain why that bug contains ~50 reports that seem entirely
> unrelated?

These are some unfortunate effects of syzbot trying to deduplicate
bugs. There's a tradeoff between reporting every single crash
separately and grouping together those that have e.g. the same origin.
Applying this algorithm transitively results in bigger clusters
containing unwanted reports.
We'll look closer.

> AIUI, this actual issue has not been reproduced since
> 2020??

Oh, sorry, I misread the table and misinformed you. The topmost row of
the table is indeed the _oldest_ one.
Another manifestation of the bug was on 2023/05/23
(https://syzkaller.appspot.com/text?tag=CrashReport&x=146f66b1280000)


>
> > Config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=ee5f7a0b2e48ed66
> > Report: https://syzkaller.appspot.com/text?tag=CrashReport&x=1325260d900000
> > Syz repro: https://syzkaller.appspot.com/text?tag=ReproSyz&x=11af973e900000
> > C repro: https://syzkaller.appspot.com/text?tag=ReproC&x=163a1e45900000
> >
> > The bug is reproducible for me locally as well (and Tetsuo's patch
> > makes it disappear, although I have no opinion on its correctness).
>
> What I'd like to do is run a kernel plus initrd locally in OVMF and
> reproduce the issue - can I do that without all the syzkaller
> machinery?

You can build the kernel from the config linked above, that's what I
did to reproduce it locally.
As for initrd, there are disk images attached to the reports, will that help?

E.g.
  $ wget https://storage.googleapis.com/syzbot-assets/79bb4ff7cc58/disk-f93f2fed.raw.xz
  $ unxz disk-f93f2fed.raw.xz
  $ qemu-system-x86_64 -smp 2,sockets=2,cores=1 -m 4G -drive
file=disk-f93f2fed.raw -snapshot -nographic -enable-kvm

lets me boot syzkaller with the disk/kernel from that report of 2023/05/23.
Adding "-net user,hostfwd=tcp::10022-:22 -net nic,model=e1000" I am
also able to SSH into the machine (there's no password):

$ ssh -o "StrictHostKeyChecking no"  -p 10022     root@...alhost

Then the repro can be downloaded and executed:

$ wget "https://syzkaller.appspot.com/text?tag=ReproC&x=163a1e45900000" -O t.c
$ gcc t.c -static -o t
$ scp -o "StrictHostKeyChecking no" -P 10022   t  root@...alhost:
$ ssh -o "StrictHostKeyChecking no"  -p 10022     root@...alhost ./t

Within a couple minutes the kernel crashes with the report:

[  151.522472][ T5865] =====================================================
[  151.523843][ T5865] BUG: KMSAN: uninit-value in aes_encrypt+0x15cc/0x1db0
[  151.525120][ T5865]  aes_encrypt+0x15cc/0x1db0
[  151.526113][ T5865]  aesti_encrypt+0x7d/0xf0
[  151.527057][ T5865]  crypto_cipher_encrypt_one+0x112/0x200
[  151.528224][ T5865]  crypto_cbcmac_digest_update+0x301/0x4b0

The vmlinux binary (also available at the syzbot page) can be used to
symbolize this report, but perhaps at this point you'd love to switch
to your own kernel.

--
Alexander Potapenko
Software Engineer

Google Germany GmbH
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