The CDC-ECM specification [1] requires to send the host MAC address as an uppercase hexadecimal string in chapter "5.4 Ethernet Networking Functional Descriptor": The Unicode character is chosen from the set of values 30h through 39h and 41h through 46h (0-9 and A-F).
However, snprintf(.., "%pm", ..) generates a lowercase MAC address string. While most host drivers are tolerant to this, UsbNcm.sys on Windows 10 is not. Instead it uses a different MAC address with all bytes set to zero including and after the first byte containing a lowercase letter. On Windows 11 Microsoft fixed it, but apparently they did not backport the fix.
This change fixes the issue by using "%pmU" to generate an uppercase hex string to comply with the specification.
[1]: https://www.usb.org/document-library/class-definitions-communication-devices..., file ECM120.pdf
Fixes: bcd4a1c40bee ("usb: gadget: u_ether: construct with default values and add setters/getters") Cc: stable@vger.kernel.org Signed-off-by: Konrad Gräfe k.graefe@gateware.de ---
Changes since v3: None
Changes since v2: * Add uppercase MAC address format string and use that instead of manually uppercasing the resulting MAC address string.
Changes since v1: * Fixed checkpatch.pl warnings
drivers/usb/gadget/function/u_ether.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c index 6956ad8ba8dd..70e6b825654c 100644 --- a/drivers/usb/gadget/function/u_ether.c +++ b/drivers/usb/gadget/function/u_ether.c @@ -963,7 +963,7 @@ int gether_get_host_addr_cdc(struct net_device *net, char *host_addr, int len) return -EINVAL;
dev = netdev_priv(net); - snprintf(host_addr, len, "%pm", dev->host_mac); + snprintf(host_addr, len, "%pmU", dev->host_mac);
return strlen(host_addr); }