Hi, Greg, Alan, All, On 05/18/2013 06:17 PM, Greg KH wrote: > On Sat, May 18, 2013 at 12:14:08PM -0400, Alan Stern wrote: >> On Sat, 18 May 2013, Hans de Goede wrote: >>> But the sysfs descriptors file will just packs the >>> rawdescriptors one behind the other, using >>> usb_device->config[x].desc.wTotalLength, where as >>> userspace only sees the length advertised by >>> the rawdescriptors, which may be different, and when >>> it is userspace will this have no idea where the next >>> descriptor starts. >>> >>> I believe the proper way to fix this is to make the >>> sysfs code deal with this the same way the usbfs code >>> does (filling the holes with 0 to avoid leaking kmem), >>> if people agree I can write a patch for this. >> >> That's okay with me. > > Sounds good to me as well.
Thanks for the input. I've been thinking about this some-more, and I see a possible other solution which I think we need to consider. Although the config.wTotalLength value in /sys/.../descriptors can not be trusted, the kernel does sanitize things to such a degree that the standard descriptor header bLength can be trusted to always be valid inside /sys/.../descriptors, so alternatively to using config.wTotalLength userspace could simple parse things one descriptor at a time, until it encounters another config descriptor or EOF, and reliable figure out where the next config descriptor starts that way. I'm sort of tending towards using that solution instead Advantages: 1) If libusb is modified to do thing this way it will work with older kernels, without needing to switch to using usbfs (which in some rough benchmarks I've run turns out to be 7 times as slow when it comes to open file, read desc, close file). 2) We're not breaking the kernel ABI, which technically my other proposal does. I know devices with multiple configs are rare, and one could argue the old behavior is a bug, but we may have something out there depending on it. Disadvantages: 1) It means that there will be some inconsistencies to how this is handled between usbfs and sysfs (note there already is such an inconsistency with regards to the endian-ness of the device descriptor). As said I tend towards using the alternative proposal I've just suggested, input very much welcome! Either way I noticed that descriptors is absent from Documentation/ABI/testing/sysfs-bus-usb Once we've a decision on which way to go, I'll document the behavior there. Regards, Hans ------------------------------------------------------------------------------ AlienVault Unified Security Management (USM) platform delivers complete security visibility with the essential security capabilities. Easily and efficiently configure, manage, and operate all of your security controls from a single console and one unified framework. Download a free trial. http://p.sf.net/sfu/alienvault_d2d _______________________________________________ libusbx-devel mailing list libusbx-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libusbx-devel
