Date: Thu, 2 Jul 2020 12:06:55 +0200 From: Jan Behrens <jbe-mlist@magnetkern.de> To: Hans Petter Selasky <hps@selasky.org> Cc: "freebsd-usb@FreeBSD.org" <freebsd-usb@freebsd.org> Subject: Re: USB reset fails when using a LimeSDR Mini on FreeBSD Message-ID: <20200702120655.73d1111e2de81c626be78139@magnetkern.de> In-Reply-To: <9e14575a-5c8b-28c8-6593-22019a21e7e7@selasky.org> References: <20200625121052.e9f7e7cbeb68fad264ec80a9@magnetkern.de> <0ec3e5a3-7f31-d1cd-6862-6066c431aa80@selasky.org> <20200626135151.e5542cf97fad213c4ad661f2@magnetkern.de> <5c0729f9-9e98-52f7-a5cb-6c5dfd2287a3@selasky.org> <20200626172851.872f3a08fa6e632666683230@magnetkern.de> <CAM8r67AF%2BfGiqBr9A0863Za_zR-fG1FxGfNAqEvvafW=wTRmyQ@mail.gmail.com> <20200627144419.f14371695d9b62ea99106c4a@magnetkern.de> <CAM8r67DTKdj0%2BhkOegjBj-ywzWFq2CnS2sQed0mibSUeGp6HSQ@mail.gmail.com> <20200627173604.7f7b7777140e66dbad812fc7@magnetkern.de> <CAM8r67DqZzje=JnrT_R3d6Uo_NxjvGsvpydd1NOTrJHU2jHzQA@mail.gmail.com> <20200627180420.4b8012fb@ernst.home> <20200702103523.adb0566bcc7b6e354905a8a5@magnetkern.de> <97c8fd11-9200-dff7-4c68-b0b80cc44871@selasky.org> <20200702104743.223e98c325806025704703f2@magnetkern.de> <e3bd0417-c89c-5598-448e-33ec1e505a3f@selasky.org> <20200702111538.e7edf0ae8d10ec7ede9acebb@magnetkern.de> <9e14575a-5c8b-28c8-6593-22019a21e7e7@selasky.org>
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On Thu, 2 Jul 2020 11:23:32 +0200 Hans Petter Selasky <hps@selasky.org> wrote: > On 2020-07-02 11:15, Jan Behrens wrote: > > On Thu, 2 Jul 2020 10:54:27 +0200 > > Hans Petter Selasky <hps@selasky.org> wrote: > > > >> On 2020-07-02 10:47, Jan Behrens wrote: > >>> But wouldn't both drivers require access to the entries in /dev ? > >> > >> Yes, user-space drivers would require access to /dev, yes, but kernel > >> drivers not, like mouse, keyboard, storage, network. > >> > >>> Thus not every user could mess with any USB device, or do I get it > >>> wrong? > >> > >> A so-called composite USB device may appear like a USB storage device > >> (kernel driver) and a security token (firefox). Firefox can only grab > >> the device if you set the proper permissions for /dev of course, but the > >> reset device IOCTL then also becomes possible, which is why we currently > >> block it for non-root. > >> > >> --HPS > > > > Okay, so if I understand it right, the problem is due to devices that > > shall be partly accessible by root, and partly by users. Some device > > nodes (e.g. /dev/usb/2.2.1 ) while others (e.g. /dev/usr/2.2.2 ) are > > limited to root access only. An USB reset always affects all devices > > (e.g. also /dev/usb/2.2.2, 2.2.3, etc.), right? > > Yes, correct. Does /dev/usb/2.2.0 (in the given example) represent the device as a whole, or is it just another subdevice? (What's the correct term for "subdevice" in this context by the way? I assume "interface"?) I experienced that /dev/usb/2.2.0 and /dev/usb/2.2.1, 2.2.2, 2.2.3, etc. get treated differently when I reset the LimeSDR Mini with "usbconfig -u 2 -a 2 reset". The devices 2.2.1 and up are supposingly re-created (and have their access rights reset), while the device 2.2.0 maintains any manually changed access rights. Is it correct that 2.2.0 identifies the device as a whole? Or is this just the first/default interface? Is there any node in the /dev filesystem, which semantically refers to the whole hardware device? > > > Disregarding implementation complexity, I'd say that resetting a USB > > device should only be possible if a user has access to all sub-devices > > (or even better to a special device node that represents the device as > > a whole). > > Maybe we can check if any kernel side drivers are attached at the time > of reset device. It might be racy, because kernel drivers can be loaded > and attached at any time. But it will work. > > What do you think? I'm not sure if this is (from a semantic point of view) the best thing to do. I would say you should only be able to reset a device if you have been granted access to the device as a whole (including all interfaces/subdevices/whatever), as the reset seems to affect all of those. > > > > > That sounds better than adding a sysctl option to me. But I assume that > > would require a lot of changes in the code? > > If a simple rule can be formulated, I could implement it in the generic > USB kernel code. > > --HPS Regards, Jan
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