SELinux: don't check permissions for kernel mounts

Don't bother checking permissions when the kernel performs an
internal mount, as this should always be allowed.
Signed-off-by: James Morris <jmorris@namei.org>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>

security/selinux/hooks.c

@@ -2484,6 +2484,10 @@ static int selinux_sb_kern_mount(struct super_block *sb, int flags, void *data)
 	if (rc)
 		return rc;
 
+	/* Allow all mounts performed by the kernel */
+	if (flags & MS_KERNMOUNT)
+		return 0;
+
 	AVC_AUDIT_DATA_INIT(&ad, FS);
 	ad.u.fs.path.dentry = sb->s_root;
 	return superblock_has_perm(cred, sb, FILESYSTEM__MOUNT, &ad);