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, 15 insertions, 0 deletions

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index c8893f663470..39eea07c2900 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -371,6 +371,11 @@ __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
 			     struct poll_table_struct *pt);
 void kernfs_notify(struct kernfs_node *kn);
 
+int kernfs_security_xattr_get(struct kernfs_node *kn, const char *suffix,
+			      void *value, size_t size);
+int kernfs_security_xattr_set(struct kernfs_node *kn, const char *suffix,
+			      void *value, size_t size, int flags);
+
 const void *kernfs_super_ns(struct super_block *sb);
 int kernfs_get_tree(struct fs_context *fc);
 void kernfs_free_fs_context(struct fs_context *fc);
@@ -473,6 +478,16 @@ static inline int kernfs_setattr(struct kernfs_node *kn,
 
 static inline void kernfs_notify(struct kernfs_node *kn) { }
 
+static inline int kernfs_security_xattr_get(struct kernfs_node *kn,
+					    const char *suffix, void *value,
+					    size_t size)
+{ return -ENOSYS; }
+
+static inline int kernfs_security_xattr_set(struct kernfs_node *kn,
+					    const char *suffix, void *value,
+					    size_t size, int flags)
+{ return -ENOSYS; }
+
 static inline const void *kernfs_super_ns(struct super_block *sb)
 { return NULL; }