usb: gadget: ncm: Avoid dropping datagrams of properly parsed NTBs

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: ncm: Avoid dropping datagrams of properly parsed NTBs

It is observed sometimes when tethering is used over NCM with Windows 11

as host, at some instances, the gadget_giveback has one byte appended at

the end of a proper NTB. When the NTB is parsed, unwrap call looks for

any leftover bytes in SKB provided by u_ether and if there are any pending

bytes, it treats them as a separate NTB and parses it. But in case the

second NTB (as per unwrap call) is faulty/corrupt, all the datagrams that

were parsed properly in the first NTB and saved in rx_list are dropped.

Adding a few custom traces showed the following:

[002] d..1 7828.532866: dwc3_gadget_giveback: ep1out:

req 000000003868811a length 1025/16384 zsI ==> 0

[002] d..1 7828.532867: ncm_unwrap_ntb: K: ncm_unwrap_ntb toprocess: 1025

[002] d..1 7828.532867: ncm_unwrap_ntb: K: ncm_unwrap_ntb nth: 1751999342

[002] d..1 7828.532868: ncm_unwrap_ntb: K: ncm_unwrap_ntb seq: 0xce67

[002] d..1 7828.532868: ncm_unwrap_ntb: K: ncm_unwrap_ntb blk_len: 0x400

[002] d..1 7828.532868: ncm_unwrap_ntb: K: ncm_unwrap_ntb ndp_len: 0x10

[002] d..1 7828.532869: ncm_unwrap_ntb: K: Parsed NTB with 1 frames

In this case, the giveback is of 1025 bytes and block length is 1024.

The rest 1 byte (which is 0x00) won't be parsed resulting in drop of

all datagrams in rx_list.

Same is case with packets of size 2048:

[002] d..1 7828.557948: dwc3_gadget_giveback: ep1out:

req 0000000011dfd96e length 2049/16384 zsI ==> 0

[002] d..1 7828.557949: ncm_unwrap_ntb: K: ncm_unwrap_ntb nth: 1751999342

[002] d..1 7828.557950: ncm_unwrap_ntb: K: ncm_unwrap_ntb blk_len: 0x800

Lecroy shows one byte coming in extra confirming that the byte is coming

in from PC:

Transfer 2959 - Bytes Transferred(1025) Timestamp((18.524 843 590)

- Transaction 8391 - Data(1025 bytes) Timestamp(18.524 843 590)

--- Packet 4063861

Data(1024 bytes)

Duration(2.117us) Idle(14.700ns) Timestamp(18.524 843 590)

--- Packet 4063863

Data(1 byte)

Duration(66.160ns) Time(282.000ns) Timestamp(18.524 845 722)

According to Windows driver, no ZLP is needed if wBlockLength is non-zero,

because the non-zero wBlockLength has already told the function side the

size of transfer to be expected. However, there are in-market NCM devices

that rely on ZLP as long as the wBlockLength is multiple of wMaxPacketSize.

To deal with such devices, it pads an extra 0 at end so the transfer is no

longer multiple of wMaxPacketSize.