usbdevice: hid_prepare() writes text instead of binary HID report descriptor

[frankurcrazy]

Bug Description

The hid_prepare() function in /usr/bin/usbdevice uses echo -ne to write the HID report descriptor:

echo -ne "\\x05\\x01\\x09\\x06..." > report_desc

On systems where /bin/sh is dash (not bash), echo does not support the -ne flags. It outputs -ne and the \x escape sequences as literal text instead of binary bytes.

The report descriptor file ends up containing:

00000000: 2d6e 6520 5c78 3035 5c78 3031  -ne \x05\x01

Instead of the correct binary:

00000000: 0501 0906 a101 0507              ........

Impact

• The USB host cannot parse the HID descriptor during enumeration
• The host sends infinite bus resets, UDC state stuck at default
• Writes to /dev/hidg0 block indefinitely
• HID keyboard emulation is completely non-functional

Fix

Replace echo -ne with printf using octal escapes (hex escapes also don't work in dash's printf):

hid_prepare()
{
	printf '\005\001\011\006\241\001\005\007\031\340\051\347\025\000\045\001\165\001\225\010\201\002\225\001\165\010\201\003\225\005\165\001\005\010\031\001\051\005\221\002\225\001\165\003\221\003\225\006\165\010\025\000\045\145\005\007\031\000\051\145\201\000\300' > report_desc
	echo 1 > protocol
	echo 1 > subclass
	echo 8 > report_length
}

Environment

• Board: RK3588 (LubanCat)
• Kernel: 5.10.160
• /bin/sh → dash