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    Subjectmount_pseudo(), sget() and MS_KERNMOUNT
    Hello,

    With Linux 4.8, the sget() function in fs/super.c got a new permission
    check: It now returns -EPERM if
    (!(flags & MS_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN)) .

    I presume the first half is intented to detect in-kernel mounts? If so,
    why doesn't mount_pseudo() (in fs/libfs.c) pass the MS_KERNMOUNT flag
    to sget()?

    This behaviour has caused a problem for me: During graphics driver
    initalization, drm_fs_inode_new() (in drivers/gpu/drm/drm_drv.c) calls
    simple_pin_fs(). The MS_KERNMOUNT flag is indeed passed down the
    call chain from there, but it is lost when mount_pseudo() is called, as
    that function doesn't take a 'flags' argument.

    Hence, the first part of the above permission check fails. (The second
    part also fails under some cicumstances due to a SELinux quirk, and
    therefore the initalization of my graphics driver doesn't succeed.)

    Regards,
    Luis Ressel

    (Apologies if I'm sending this inquiry to the wrong people. I don't
    know much about the kernel development workflow, so I decided to send
    it to whomever get_maintainer.pl spat out, plus the author of the
    sget() change in 4.8.)

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