Hi, Some months ago I raised my concerns about artificial limits in usbfs, by submitting two very simple patches:
http://article.gmane.org/gmane.linux.usb.devel/40811 http://article.gmane.org/gmane.linux.usb.devel/40812 The issue hasn't been resolved yet, so I'd like to briefly restate the points made thus far and solicit any further comments on the issue. The proc_do_submiturb() implementation in devio.c tests URBs against several arbitrary limits. The two I'm most concerned about are: 1. /* min 8 byte setup packet, max arbitrary */ if (uurb->buffer_length < 8 || uurb->buffer_length > PAGE_SIZE) return -EINVAL; 2. if (isopkt[u].length > 1023) { kfree(isopkt); return -EINVAL; } The limit in (1) makes it impossible to write userspace drivers for devices which require a full 4K of data in their control transfers. The limit in (2) makes it impossible to support high-bandwidth USB 2.0 isochronous transfers from userspace. My solution was to bump (1) from PAGE_SIZE to PAGE_SIZE*2, and (2) from 1023 to 6144, but both suggestions were relatively arbitrary. David Brownell suggested replacing the limit in (1) with 4K+8 bytes, and he pointed out that the test in (2) should respect the device's descriptors. That started a discussion on whether the tests in devio.c should enforce validity according to the USB spec, or whether they should simply prevent userspace code from causing overflows or unusually large kmalloc()s. I would submit that it isn't the usbfs layer's job to enforce the USB spec. There are two reasons for this: - Some USB devices are broken, and it should still be possible to write drivers for them on Linux- even user-space drivers. - Any portions of the USB spec that Linux does choose to enforce should be enforced in the main URB submit paths, rather than at the usbfs layer. The class of URBs which kernel code can submit but userlevel code cannot submit should be limited only to those which have a danger of affecting system stability. I'd be very interested to hear more opinions on this issue. --Micah ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid0709&bid&3057&dat1642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
