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.)
