What would be a simpler way to do this so that the guest machine would still be able to recognize the USB drive? Right now we're triggering a script whenever udev recognizes that a USB drive is plugged in. The script copies the allowed files to a certain folder. The guest has a cron job that periodically triggers scp from that folder to the guest. That's a very complicated flow and I just described only the flow which files are imported. I even omitted some of the moving parts since they are irrelevant. Long story short our architecture is very complicated because of this issue.
On Wed, Apr 25, 2018, 7:17 PM Bandan Das <b...@redhat.com> wrote: > Omer Katz <o...@kazuar-tech.com> writes: > > > We're connecting USB drives that we want the guests to copy files from. > > The user should only be allowed to copy certain files into the system. > > The same thing goes for copying files to the USB drive. We only allow > > certain files to be exported from the guest. > > If I understand your problem correctly, this should be doable by plugging > in > your logic into usb_mtp_write_data for the write side and > usb_mtp_handle_data > for the read side. The write probably doesn't need a lot, you trigger an > error > response the moment your data has something you don't want and discard the > new file. > For the read, though, you probably have to read the whole file first, > which is not what the current code is doing (I think). > > Apart from that dev-mtp.c is implementing a MTP server based on the MTP > spec and adding > something like this would be confusing, I also feel that this is too > specific a usecase > and as Daniel said, there are perhaps simpler ways of doing it. > > Bandan > > > On Wed, Apr 25, 2018, 12:57 PM Daniel P. Berrangé <berra...@redhat.com> > > wrote: > > > >> On Mon, Apr 23, 2018 at 03:10:32PM +0000, Omer Katz wrote: > >> > Hi everyone, > >> > > >> > We have a use case that requires us to only allow certain files to > pass > >> > through to the guest machine from USB storage devices. > >> > > >> > I was told on IRC that such a feature does not exist but the easiest > way > >> to > >> > achieve our goal is to contribute a patch the the MTP device driver > since > >> > other drivers operate on a filesystem level instead of a file level > which > >> > is what we need. > >> > >> IMHO the easiest way to stop the guest accessing files is to simply not > >> put them in the directory that you are exporting the guest in the first > >> place. If you have a directory that has some files you don't want > accessed > >> and can't remove them, then perhaps create a second directory and use > >> symlinks or hardlinks to pull in files from the original directory. > >> > >> > The plan is to pass the contents of each file to a program through > stdin > >> > and decide based on the exit code if the file should be allowed to > pass > >> > through to the guest or not. > >> > >> I can't say I like this idea. It is a really very inefficient and heavy > >> solution. > >> > >> > Since this is the first time I'm contributing to QEMU I'd like some > >> > guidance to where the filtering code should be. > >> > https://github.com/qemu/qemu/blob/master/hw/usb/dev-mtp.c doesn't > look > >> that > >> > complicated but I still need to understand it better to continue. > >> > Furthermore, I need to know where to add such a command line option to > >> > point QEMU to the filtering program. > >> > > >> > Would such a patch be accepted if all the requirements above are met? > >> > >> Can you explain the usage scenario you have in more details, rather than > >> just the high level abstract. > >> > >> > >> Regards, > >> Daniel > >> -- > >> |: https://berrange.com -o- > >> https://www.flickr.com/photos/dberrange :| > >> |: https://libvirt.org -o- > >> https://fstop138.berrange.com :| > >> |: https://entangle-photo.org -o- > >> https://www.instagram.com/dberrange :| > >> >