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Date: Tue, 2 Jan 2024 08:03:36 +0000
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Krishna Kurapati <quic_kriskura@quicinc.com>
Cc: Maciej =?utf-8?Q?=C5=BBenczykowski?= <maze@google.com>,
	Hardik Gajjar <hgajjar@de.adit-jv.com>, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, quic_ppratap@quicinc.com,
	quic_wcheng@quicinc.com, quic_jackp@quicinc.com
Subject: Re: [PATCH] usb: gadget: ncm: Avoid dropping datagrams of properly
 parsed NTBs
Message-ID: <2024010223-snore-unbolted-dc68@gregkh>
References: <20240102055143.3889-1-quic_kriskura@quicinc.com>
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In-Reply-To: <20240102055143.3889-1-quic_kriskura@quicinc.com>

On Tue, Jan 02, 2024 at 11:21:43AM +0530, Krishna Kurapati wrote:
> 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)
> 
> Fix this by checking if the leftover bytes before parsing next NTB is of
> size more than the expected header.
> 
> Fixes: 427694cfaafa ("usb: gadget: ncm: Handle decoding of multiple NTB's in unwrap call")
> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
> ---
> There could probably be cases where the first NTB is proper and the second
> NTB's header is proper but the NDP is corrupt, and in those cases too, all
> the datagrams are dropped. But I haven't seen such case practically.
> 
>  drivers/usb/gadget/function/f_ncm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- You have marked a patch with a "Fixes:" tag for a commit that is in an
  older released kernel, yet you do not have a cc: stable line in the
  signed-off-by area at all, which means that the patch will not be
  applied to any older kernel releases.  To properly fix this, please
  follow the documented rules in the
  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot