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Sat, 15 Mar 2025 11:40:42 -0700 (PDT) Date: Sat, 15 Mar 2025 14:40:38 -0400 From: Alan Stern To: daixin_tkzc Cc: Matthew Dharm , Greg KH , linux-usb@vger.kernel.org, usb-storage@lists.one-eyed-alien.net, linux-kernel@vger.kernel.org Subject: Re: Re: Re: [usb-storage] Re:Re:[PATCH] usb: storage: Fix `us->iobuf` size for BOT transmission to prevent memory overflow Message-ID: <6b4fe6ca-e18b-4843-aeaf-224ee01d3067@rowland.harvard.edu> References: <20250311084111.322351-1-daixin_tkzc@163.com> <2b6c4aa7.b165.1958f6b7a3a.Coremail.daixin_tkzc@163.com> <814316b6-013b-4735-995d-b6c0c616c71b@rowland.harvard.edu> <1681f087.2727.195927b7ccb.Coremail.daixin_tkzc@163.com> <516c8f89-45f2-4d3f-b1e7-29aecfc8cd3c@rowland.harvard.edu> <6e125c5c.2541.195990d2daa.Coremail.daixin_tkzc@163.com> <265533ba.2e97.1959988d8b1.Coremail.daixin_tkzc@163.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <265533ba.2e97.1959988d8b1.Coremail.daixin_tkzc@163.com> On Sat, Mar 15, 2025 at 07:20:37PM +0800, daixin_tkzc wrote: > I'm sorry you may have misunderstood me. > > > HCTSIZ register only reflects the transfer size for the Host Channel (between host and device). The dwc_otg manual explains it as follows： > Non-Scatter/Gather DMA Mode: > Transfer Size (XferSize) > For an OUT, this field is the number of data bytes the host sends > during the transfer. > For an IN, this field is the buffer size that the application has > Reserved for the transfer. The application is expected to program > this field as an integer multiple of the maximum packet size for IN > transactions (periodic and non-periodic). In that case, the dwc_otg driver needs to use a 512-byte bounce buffer. The driver must _guarantee_ that no more than 13 bytes will be written to the URB's transfer_buffer if the URB's transfer_length is 13. If the hardware cannot provide this guarantee then the driver must work around the hardware's deficiencies. That is how the kernel's USB API is designed. Alan Stern