CVE-2024-27405: 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 gadgetgiveback 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 uether 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 rxlist are dropped.

Adding a few custom traces showed the following: [002] d..1 7828.532866: dwc3gadgetgiveback: ep1out: req 000000003868811a length 1025/16384 zsI ==> 0 [002] d..1 7828.532867: ncmunwrapntb: K: ncmunwrapntb toprocess: 1025 [002] d..1 7828.532867: ncmunwrapntb: K: ncmunwrapntb nth: 1751999342 [002] d..1 7828.532868: ncmunwrapntb: K: ncmunwrapntb seq: 0xce67 [002] d..1 7828.532868: ncmunwrapntb: K: ncmunwrapntb blklen: 0x400 [002] d..1 7828.532868: ncmunwrapntb: K: ncmunwrapntb ndplen: 0x10 [002] d..1 7828.532869: ncmunwrapntb: 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 rxlist.

Same is case with packets of size 2048: [002] d..1 7828.557948: dwc3gadgetgiveback: ep1out: req 0000000011dfd96e length 2049/16384 zsI ==> 0 [002] d..1 7828.557949: ncmunwrapntb: K: ncmunwrapntb nth: 1751999342 [002] d..1 7828.557950: ncmunwrapntb: K: ncmunwrapntb blklen: 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.