From: Oliver Neukum <oneukum@suse.com>
To: "Bjørn Mork" <bjorn@mork.no>,
syzbot <syzbot+0631d878823ce2411636@syzkaller.appspotmail.com>
Cc: 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 12:15:16 +0100 [thread overview]
Message-ID: <1572952516.2921.6.camel@suse.com> (raw)
In-Reply-To: <87ftj32v6y.fsf@miraculix.mork.no>
Am Montag, den 04.11.2019, 22:22 +0100 schrieb Bjørn Mork:
> This looks like a false positive to me. max_datagram_size is two bytes
> declared as
>
> __le16 max_datagram_size;
>
> and the code leading up to the access on drivers/net/usb/cdc_ncm.c:587
> is:
>
> /* read current mtu value from device */
> err = usbnet_read_cmd(dev, USB_CDC_GET_MAX_DATAGRAM_SIZE,
> USB_TYPE_CLASS | USB_DIR_IN | USB_RECIP_INTERFACE,
> 0, iface_no, &max_datagram_size, 2);
At this point err can be 1.
> if (err < 0) {
> dev_dbg(&dev->intf->dev, "GET_MAX_DATAGRAM_SIZE failed\n");
> goto out;
> }
>
> if (le16_to_cpu(max_datagram_size) == ctx->max_datagram_size)
>
>
>
> AFAICS, there is no way max_datagram_size can be uninitialized here.
> usbnet_read_cmd() either read 2 bytes into it or returned an error,
No. usbnet_read_cmd() will return the number of bytes transfered up
to the number requested or an error.
> causing the access to be skipped. Or am I missing something?
Yes. You can get half the MTU. We have a similar class of bugs
with MAC addresses.
Regards
Oliver
next prev parent reply other threads:[~2019-11-05 11:31 UTC|newest]
Thread overview: 9+ 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 [this message]
2019-11-05 12:25 ` Bjørn Mork
2019-11-05 13:51 ` Oliver Neukum
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
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