From: Oliver Neukum <oneukum@suse.com>
To: "Bjørn Mork" <bjorn@mork.no>
Cc: syzbot <syzbot+0631d878823ce2411636@syzkaller.appspotmail.com>,
davem@davemloft.net, glider@google.com,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: KMSAN: uninit-value in cdc_ncm_set_dgram_size
Date: Tue, 05 Nov 2019 14:51:19 +0100 [thread overview]
Message-ID: <1572961879.2921.13.camel@suse.com> (raw)
In-Reply-To: <875zjy33z2.fsf@miraculix.mork.no>
Am Dienstag, den 05.11.2019, 13:25 +0100 schrieb Bjørn Mork:
> Oliver Neukum <oneukum@suse.com> writes:
> > Am Montag, den 04.11.2019, 22:22 +0100 schrieb Bjørn Mork:
> Ah, OK. So that could be fixed with e.g.
>
> if (err < 2)
> goto out;
>
>
> Or would it be better to add a strict length checking variant of this
> API? There are probably lots of similar cases where we expect a
We would lose flexibilty and the check needs to be there anyway.
> Right. And probably all 16 or 32 bit integer reads...
>
> Looking at the NCM spec, I see that the wording is annoyingly flexible
> wrt length - both ways. E.g for GetNetAddress:
>
> To get the entire network address, the host should set wLength to at
> least 6. The function shall never return more than 6 bytes in response
> to this command.
>
> Maybe the correct fix is simply to let usbnet_read_cmd() initialize the
> full buffer regardless of what the device returns? I.e.
This issue has never been observed in the wild. We are defending
against a possible attack. It is better to react drastically.
> at do you think?
>
> Personally, I don't think it makes sense for a device to return a 1-byte
> mtu or 3-byte mac address. But the spec allows it and this would at
> least make it safe.
Hence we should ignore such a reply. The support is optional anyway.
For usbnet as such, however, we cannot really hardcode the size of
a MAC.
Regards
Oliver
next prev parent reply other threads:[~2019-11-05 13:51 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-30 19:22 KMSAN: uninit-value in cdc_ncm_set_dgram_size syzbot
2019-11-04 21:22 ` Bjørn Mork
2019-11-05 11:15 ` Oliver Neukum
2019-11-05 12:25 ` Bjørn Mork
2019-11-05 13:51 ` Oliver Neukum [this message]
2019-11-05 13:55 ` Alexander Potapenko
2019-11-05 15:35 ` Greg Kroah-Hartman
2019-11-05 11:11 ` Oliver Neukum
2019-11-05 12:51 ` syzbot
2019-11-06 12:23 ` Oliver Neukum
2019-11-06 16:31 ` syzbot
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