From: Konrad Gräfe <k.graefe@xxxxxxxxxxx>
commit 3c0f4f09c063e143822393d99cb2b19a85451c07 upstream.
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 upper-casing the MAC to comply with the
specification.
[1]: https://www.usb.org/document-library/class-definitions-communication-devices-12, file ECM120.pdf
Fixes: bcd4a1c40bee ("usb: gadget: u_ether: construct with default values and add setters/getters")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Konrad Gräfe <k.graefe@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230505143640.443014-1-k.graefe@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/gadget/function/u_ether.c | 3 +++
1 file changed, 3 insertions(+)
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -18,6 +18,7 @@
#include <linux/ethtool.h>
#include <linux/if_vlan.h>
#include <linux/etherdevice.h>
+#include <linux/string_helpers.h>
#include "u_ether.h"
@@ -976,6 +977,8 @@ int gether_get_host_addr_cdc(struct net_
dev = netdev_priv(net);
snprintf(host_addr, len, "%pm", dev->host_mac);
+ string_upper(host_addr, host_addr);
+
return strlen(host_addr);
}
EXPORT_SYMBOL_GPL(gether_get_host_addr_cdc);
