On Mon, Mar 23, 2020 at 10:21 AM Bobby Jones [off-list ref] wrote:

Hello net-dev,

I'm diagnosing a problem with the Toby MPCI-L201 cellular modem where
http operations hang. This is reproducible on the most recent kernel
by turning on the rndis_host driver and executing a wget or similar
http command. I found I was able to still ping but not transfer any
data. After bisecting I've found that commit
a5a18bdf7453d505783e40e47ebb84bfdd35f93b introduces this hang.

For reference the patch contents are:

quoted

    rndis_host: Set valid random MAC on buggy devices

    Some devices of the same type all export the same, random MAC address. This
    behavior has been seen on the ZTE MF910, MF823 and MF831, and there are
    probably more devices out there. Fix this by generating a valid random MAC
    address if we read a random MAC from device.

    Also, changed the memcpy() to ether_addr_copy(), as pointed out by
    checkpatch.

    Suggested-by: Bjørn Mork [off-list ref]
    Signed-off-by: Kristian Evensen [off-list ref]
    Signed-off-by: David S. Miller [off-list ref]

diff --git a/drivers/net/usb/rndis_host.c b/drivers/net/usb/rndis_host.c
index 524a47a28120..4f4f71b2966b 100644
--- a/drivers/net/usb/rndis_host.c
+++ b/drivers/net/usb/rndis_host.c

@@ -428,7 +428,11 @@ generic_rndis_bind(struct usbnet *dev, struct usb_interface *intf, int flags)
                dev_err(&intf->dev, "rndis get ethaddr, %d\n", retval);
                goto halt_fail_and_release;
        }
-       memcpy(net->dev_addr, bp, ETH_ALEN);
+
+       if (bp[0] & 0x02)
+               eth_hw_addr_random(net);
+       else
+               ether_addr_copy(net->dev_addr, bp);

        /* set a nonzero filter to enable data transfers */
        memset(u.set, 0, sizeof *u.set);

I know that there is some internal routing done by the modem firmware,
and I'm assuming that overwriting the MAC address breaks said routing.
Can anyone suggest what a proper fix would be?

Thanks,
Bobby

Adding some individuals and lists in hopes for feedback