Security: add get, set, and cloning of superblock security information
Adds security_get_sb_mnt_opts, security_set_sb_mnt_opts, and security_clont_sb_mnt_opts to the LSM and to SELinux. This will allow filesystems to directly own and control all of their mount options if they so choose. This interface deals only with option identifiers and strings so it should generic enough for any LSM which may come in the future. Filesystems which pass text mount data around in the kernel (almost all of them) need not currently make use of this interface when dealing with SELinux since it will still parse those strings as it always has. I assume future LSM's would do the same. NFS is the primary FS which does not use text mount data and thus must make use of this interface. An LSM would need to implement these functions only if they had mount time options, such as selinux has context= or fscontext=. If the LSM has no mount time options they could simply not implement and let the dummy ops take care of things. An LSM other than SELinux would need to define new option numbers in security.h and any FS which decides to own there own security options would need to be patched to use this new interface for every possible LSM. This is because it was stated to me very clearly that LSM's should not attempt to understand FS mount data and the burdon to understand security should be in the FS which owns the options. Signed-off-by: Eric Paris <eparis@redhat.com> Acked-by: Stephen D. Smalley <sds@tycho.nsa.gov> Signed-off-by: James Morris <jmorris@namei.org>
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