Re: [PATCH net,stable] net: qmi_wwan: fix divide by 0 on bad descriptors

[David Miller]

From: Bjørn Mork 
Date: Mon,  6 Nov 2017 15:32:18 +0100

> A CDC Ethernet functional descriptor with wMaxSegmentSize = 0 will
> cause a divide error in usbnet_probe:
> 
> divide error:  [#1] PREEMPT SMP KASAN
 ...
> 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 
> Signed-off-by: Bjørn Mork 

Applied and queued up for -stable.
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[PATCH net,stable] net: qmi_wwan: fix divide by 0 on bad descriptors

[Bjørn Mork]

A CDC Ethernet functional descriptor with wMaxSegmentSize = 0 will
cause a divide error in usbnet_probe:

divide error:  [#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: 88006bef5c00 task.stack: 88006bf6
RIP: 0010:usbnet_update_max_qlen+0x24d/0x390 drivers/net/usb/usbnet.c:355
RSP: 0018:88006bf67508 EFLAGS: 00010246
RAX: 000163c8 RBX: 8800621fce40 RCX: 8800621fcf34
RDX:  RSI: 837ecb7a RDI: 8800621fcf34
RBP: 88006bf67520 R08: 88006bef5c00 R09: ed000c43f881
R10: ed000c43f880 R11: 8800621fc406 R12: 0003
R13: 85c71de0 R14:  R15: 
FS:  () GS:88006ca0() knlGS:
CS:  0010 DS:  ES:  CR0: 80050033
CR2: 7ffe9c0d6dac CR3: 614f4000 CR4: 06f0
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 
Signed-off-by: Bjørn Mork 
---
 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 8c3733608271..a4f229edcceb 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);
}
-- 
2.11.0

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