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
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