fchownat not respecting AT_EMPTY_PATH on file descriptors opened with O_PATH about gvisor HOT 7 CLOSED

Again, thanks for the detailed bug report and doing a lot of the debugging on our behalf. I am sending a fix.

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Small note: systemd itself, even if it were installed successfully, would probably not run in gVisor. Last time this was attempted, gVisor was still missing the implementation of some syscalls and functionality (cgroups perhaps?) to make it work properly.

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@EtiennePerot thanks for the reply. I'm not too surprised to be honest. The install of systemd was actually resulting from apt-get install npm, and it's possible that npm would work correctly if the systemd dep succeeded.

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Hmm, open(2) says:

       O_PATH (since Linux 2.6.39)
              Obtain a file descriptor that can be used for two
              purposes: to indicate a location in the filesystem tree
              and to perform operations that act purely at the file
              descriptor level.  The file itself is not opened, and
              other file operations (e.g., read(2), write(2), fchmod(2),
              fchown(2), fgetxattr(2), ioctl(2), mmap(2)) fail with the
              error EBADF.

But it seems like O_PATH FD is allowed to make fchown(2) with AT_EMPTY_PATH?

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O_PATH FD is allowed to make fchown(2) with AT_EMPTY_PATH?

Yes that's my interpretation of the open(2) and fchownat(2) docs.

AT_EMPTY_PATH (since Linux 2.6.39)
              If  pathname is an empty string, operate on the file referred to
              by dirfd (which may have been obtained using the [open(2)](http://man.he.net/man2/open)  O_PATH
              flag).
              ....

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#9468 should be the right fix.

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Nice one!

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