LSM: add new hook for kernfs node initialization

This patch introduces a new security hook that is intended for
initializing the security data for newly created kernfs nodes, which
provide a way of storing a non-default security context, but need to
operate independently from mounts (and therefore may not have an
associated inode at the moment of creation).

The main motivation is to allow kernfs nodes to inherit the context of
the parent under SELinux, similar to the behavior of
security_inode_init_security(). Other LSMs may implement their own logic
for handling the creation of new nodes.

This patch also adds helper functions to <linux/kernfs.h> for
getting/setting security xattrs of a kernfs node so that LSMs hooks are
able to do their job. Other important attributes should be accessible
direcly in the kernfs_node fields (in case there is need for more, then
new helpers should be added to kernfs.h along with the patch that needs
them).

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: more manual merge fixes]
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index a9b8ff578b6b..0dd5bda719e6 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -445,6 +445,15 @@
  *      to abort the copy up. Note that the caller is responsible for reading
  *      and writing the xattrs as this hook is merely a filter.
  *
+ * Security hooks for kernfs node operations
+ *
+ * @kernfs_init_security
+ *      Initialize the security context of a newly created kernfs node based
+ *      on its own and its parent's attributes.
+ *
+ *      @kn_dir the parent kernfs node
+ *      @kn the new child kernfs node
+ *
  * Security hooks for file operations
  *
  * @file_permission:
@@ -1578,6 +1587,9 @@ union security_list_options {
         int (*inode_copy_up)(struct dentry *src, struct cred **new);
         int (*inode_copy_up_xattr)(const char *name);
 
+        int (*kernfs_init_security)(struct kernfs_node *kn_dir,
+                                    struct kernfs_node *kn);
+
         int (*file_permission)(struct file *file, int mask);
         int (*file_alloc_security)(struct file *file);
         void (*file_free_security)(struct file *file);
@@ -1879,6 +1891,7 @@ struct security_hook_heads {
         struct hlist_head inode_getsecid;
         struct hlist_head inode_copy_up;
         struct hlist_head inode_copy_up_xattr;
+        struct hlist_head kernfs_init_security;
         struct hlist_head file_permission;
         struct hlist_head file_alloc_security;
         struct hlist_head file_free_security;