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Date: Mon, 12 Oct 2026 14:54:33 +0200
From: Andrew Lunn <andrew@lunn.ch>
To: Xinsheng Zhu <xinsheng.zhu.ny@gmail.com>
Cc: netdev@vger.kernel.org, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, andrew+netdev@lunn.ch,
	davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org,
	pabeni@redhat.com, oliver@neukum.org, giuseppe@southpole.se
Subject: Re: [PATCH net v2] net: usb: cdc_ncm: reject short
 GET_NTB_PARAMETERS responses
Message-ID: <66ef60eb-524d-46ea-b6c8-0543bb2c0c63@lunn.ch>
References: <20261011035150.53315-1-xinsheng.zhu.ny@gmail.com>
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In-Reply-To: <20261011035150.53315-1-xinsheng.zhu.ny@gmail.com>

On Sat, Oct 10, 2026 at 11:51:50PM -0400, Xinsheng Zhu wrote:
> usbnet_read_cmd() returns the actual transfer length, but cdc_ncm_init()
> only checks for negative errors when reading the NTB parameters. A short
> response therefore leaves the missing bytes zero-filled, and
> initialization continues with parameters that were not supplied by the
> device.
> 
> CDC NCM 1.1, section 7.2.1, Table 7-3 defines a 28-byte NTB
> parameter structure. Require GET_NTB_PARAMETERS to return the
> complete structure before continuing initialization.
> 
> Return -EIO for short responses, including zero-length responses, and
> preserve negative errors from usbnet_read_cmd(). This ensures that a
> zero-byte response cannot be reported as successful initialization when
> rejecting an incomplete response.
> 
> The issue is theoretical and was found by manual inspection of
> usbnet_read_cmd() callers with LLM assistance.

If this is theoretical, please drop the Fixes tag and post to
net-next.

	Andrew