ACK: [PATCH] net: qmi_wwan: fix divide by 0 on bad descriptors

[Kleber Souza]

On 07/20/18 17:59, Colin King wrote:
> From: Bjørn Mork <bjorn at mork.no>
> 
> CVE-2017-16650
> 
> A CDC Ethernet functional descriptor with wMaxSegmentSize = 0 will
> cause a divide error in usbnet_probe:
> 
> divide error: 0000 [#1] PREEMPT SMP KASAN
> Modules linked in:
> CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.14.0-rc8-44453-g1fdc1a82c34f #56
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Workqueue: usb_hub_wq hub_event
> task: ffff88006bef5c00 task.stack: ffff88006bf60000
> RIP: 0010:usbnet_update_max_qlen+0x24d/0x390 drivers/net/usb/usbnet.c:355
> RSP: 0018:ffff88006bf67508 EFLAGS: 00010246
> RAX: 00000000000163c8 RBX: ffff8800621fce40 RCX: ffff8800621fcf34
> RDX: 0000000000000000 RSI: ffffffff837ecb7a RDI: ffff8800621fcf34
> RBP: ffff88006bf67520 R08: ffff88006bef5c00 R09: ffffed000c43f881
> R10: ffffed000c43f880 R11: ffff8800621fc406 R12: 0000000000000003
> R13: ffffffff85c71de0 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff88006ca00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffe9c0d6dac CR3: 00000000614f4000 CR4: 00000000000006f0
> Call Trace:
>  usbnet_probe+0x18b5/0x2790 drivers/net/usb/usbnet.c:1783
>  qmi_wwan_probe+0x133/0x220 drivers/net/usb/qmi_wwan.c:1338
>  usb_probe_interface+0x324/0x940 drivers/usb/core/driver.c:361
>  really_probe drivers/base/dd.c:413
>  driver_probe_device+0x522/0x740 drivers/base/dd.c:557
> 
> Fix by simply ignoring the bogus descriptor, as it is optional
> for QMI devices anyway.
> 
> Fixes: 423ce8caab7e ("net: usb: qmi_wwan: New driver for Huawei QMI based WWAN devices")
> Reported-by: Andrey Konovalov <andreyknvl at google.com>
> Signed-off-by: Bjørn Mork <bjorn at mork.no>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (clean upstream cherry pick of commit 7fd078337201cf7468f53c3d9ef81ff78cb6df3b)
> Signed-off-by: Colin Ian King <colin.king at canonical.com>

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  drivers/net/usb/qmi_wwan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
> index 8c37336..a4f229e 100644
> --- a/drivers/net/usb/qmi_wwan.c
> +++ b/drivers/net/usb/qmi_wwan.c
> @@ -681,7 +681,7 @@ static int qmi_wwan_bind(struct usbnet *dev, struct usb_interface *intf)
>  	}
>  
>  	/* errors aren't fatal - we can live with the dynamic address */
> -	if (cdc_ether) {
> +	if (cdc_ether && cdc_ether->wMaxSegmentSize) {
>  		dev->hard_mtu = le16_to_cpu(cdc_ether->wMaxSegmentSize);
>  		usbnet_get_ethernet_addr(dev, cdc_ether->iMACAddress);
>  	}
>