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<cfhammar> I have discovered a bug in the dir-lookup protocol though <cfhammar> Currently, I'm investigating the bug a bit further <cfhammar> when doing dir-lookups with several path components, the look-up is done with the authority of the user who opened the directory, as opposed to the user doing the lookup <cfhammar> e.g, consider foo/bar/baz, where bar can only be used by its owner and foo and baz are world readable <cfhammar> if foo is opened, then transferred to another user, he can open baz, which he shouldn't be able to <cfhammar> this is possible where foo/bar/baz is within a single translator, and the lookup is done in a single dir-lookup <antrik> cfhammar: I'm not sure this is a bug <cfhammar> I have a test case that triggers the bug, and another that doesn't which currently confuses me <antrik> cfhammar: it's probably not very usual to pass around open directory ports; but if somebody does it, it's probably actually desired that it keeps the authority <antrik> it's kinda consistent with passing normal FDs <cfhammar> antrik: it should only allow accesses to entries not sub-entries <cfhammar> antrik: it isn't allowed in Linux atleast, and I'm guessing it's mandated by posix <cfhammar> also note that a more common scenario is a process that opens a directory and then drops authority <cfhammar> probably more common, that is <antrik> cfhammar: I'm not really familiar with directory access functions... I wasn't even aware that it's possible to pass around directory FDs <antrik> but if it is, it would indeed be good to know what POSIX says about this <antrik> cfhammar: I don't see how this is related?... <cfhammar> antrik: after the process has dropped authority it can still make lookups in directories that it should no longer be able to <antrik> cfhammar: interesting point... <antrik> cfhammar: do you think this is fixable? <cfhammar> antrik: Not without (defacto) changing the interface <cfhammar> e.g only looking up a singe path component at a time <cfhammar> or doing the auth check lazily on io_reauthenticate <antrik> cfhammar: yeah, obviously it's not possible without an API change. I just wonder whether it's possible without throwing the current auth/lookup mechanism overboard alltogether... <cfhammar> antrik: both my solutions are only minor changes to the API, but fairly major in the sense that we need to change all callers :-( <cfhammar> diskfs_S_dir_lookup is a very large function, for example <antrik> cfhammar: OK <antrik> cfhammar: I wonder whether there is a possible transition path without breaking all existing installations... <cfhammar> we could provide a new RPC while supporting the old one <cfhammar> note that changing fs.defs only affects glibc and the Hurd, normal apps should be fine <antrik> cfhammar: have you posted your findings to the ML yet? <cfhammar> No, I'm still investigating why my second test-case doesn't trigger the bug <cfhammar> Intrestingly it's the one using all POSIX functions... <cfhammar> Perhaps its a bug that maskes the lookup bug ;-) <antrik> I guess there is some quirk which you do not fully understand yet :-) <cfhammar> Oh, there's always a new quirk to find in the Hurd :-) <cfhammar> antrik: seems that dir_lookup isn't buggy after all <cfhammar> antrik: as all FDs are reauthenticated on setauth <antrik> ah <cfhammar> antrik: and (presumably) ports are unauthenticated and reauthenticated when transfered <antrik> yeah, that's the idea behind the auth protocol... <antrik> users obtain specific capabilities by authenticating generic ports against their own ID <cfhammar> I didn't really have a coherent view on how open flags are handled on reauth <cfhammar> it seems open flags always win, so that a O_READ port that is unauthed is still readable <antrik> not sure what you mean <cfhammar> if I open a file to read it, then reauth it with a user that isn't permitted to read it, I can still read from it <cfhammar> (as it should be) <cfhammar> by contrast permission to do lookups in a directory is determined by who authed it <cfhammar> so I won't be able to do lookups after a reauth, if it's not permitted by the file bits <youpi> Mmm, openat should however be able to <youpi> since you've first opened the directory with the auth <cfhammar> it isn't since open FDs are reauthed on setauth <cfhammar> not sure whether it should though, Linux behaves the same way atleast <cfhammar> though it could be done with POSIX.2008's O_SEARCH open flag