CVE-2024-27405 usb: gadget: ncm: Avoid dropping datagrams of properly parsed NTBs

2024-05-1711:40:25

Linux

github.com

usb gadget vulnerability

linux kernel

ncm

ntb parsing

tethering

windows 11

datagrams

giveback

skb

custom traces

block length

lecroy

zlp

wmaxpacketsize

cve

AI Score

6.7

Confidence

Low

EPSS

Percentile

13.0%

SSVC

Exploitation

none

Automatable

Technical Impact

total

JSON

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.

ADP Affected

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]