21.11.2019 00:51, Stephan Müller пишет: > Am Mittwoch, 20. November 2019, 14:29:18 CET schrieb Greg Kroah-Hartman: > > Hi Greg, > >> On Wed, Nov 20, 2019 at 09:58:35AM +0100, Stephan Müller wrote: >>> Am Dienstag, 19. November 2019, 13:41:50 CET schrieb Greg Kroah-Hartman: >>> >>> Hi Greg, >>> >>>> On Tue, Nov 19, 2019 at 02:07:40AM -0800, Andy Lutomirski wrote: >>>>>> As this would introduce a new device file now, is there a special >>>>>> process that I need to follow or do I need to copy? Which >>>>>> major/minor >>>>>> number should I use? >>>>>> >>>>>> Looking into static const struct memdev devlist[] I see >>>>>> >>>>>> [8] = { "random", 0666, &random_fops, 0 }, >>>>>> [9] = { "urandom", 0666, &urandom_fops, 0 }, >>>>>> >>>>>> Shall a true_random be added here with [10]? >>>>> >>>>> I am not at all an expert on chardevs, but this sounds generally >>>>> reasonable. gregkh is probably the real authority here. >>>> >>>> [10] is the aio char device node, so you better not try to overlap it or >>>> bad things will happen :( >>> >>> Thanks for your insights. >>> >>> Which device minor number could we use? >> >> Get your own dynamic one by using a misc device if you _REALLY_ want to >> add yet-another-char-node-for-random-data. >> >> But I would have thought that we all realize that this is not the way to >> do things. Let's not have "random", "urandom", and "true_random" be >> something we want to totally confuse userspace with, that way is insane. >> >> Please just make the existing userspace api "just work", don't add to >> the mess. > > Thank you, I think we should follow that advise. > > With that and considering Alexander's rightful remark we have a challenge. So, > changing the syscall may not be the right way unless we find a way to restrict > the permissions somehow (capability? LSM? None of that seems to be a good > fit). > > What about providing a /sys file? I.e. adding a file that: > > a) has permissions 440 per default and maybe the ownership of root:root > > b) allow user space to perform a chown/chgrp > > c) only supports reading of data from user space > > But then, how could we provide a common interface for the existing random.c > and the LRNG? > > Or should we use a proc file for that? If yes, I guess it should not be a > sysctl, but a "regular" proc file that should allow a chown(2) operation. On > the other hand, is proc the right place to provide a user space interface for > exporting data to user? > > Thanks a lot. > > Ciao > Stephan > > I'd say that a sys or proc file is worse than a device node, because the wanted semantics are exactly those of a device node. Besides, a chown of a sysfs file is something not friendly to containers. We may need different uids in different containers to be able to access true random data. -- Alexander E. Patrakov