[PATCH 1/5] Security: Provide copy-up security hooks for unioned files

[David Howells <dhowells@redhat.com>]

Provide two new security hooks for use with security files that are used when
a file is copied up between layers:

 (1) security_inode_copy_up().  This is called so that the security label on
     the destination file can be set appropriately.

 (2) security_inode_copy_up_xattr().  This is called so that each xattr being
     copied up can be vetted - including modification and discard.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 include/linux/lsm_hooks.h |   23 +++++++++++++++++++++++
 include/linux/security.h  |   14 ++++++++++++++
 security/security.c       |   17 +++++++++++++++++
 3 files changed, 54 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index ec3a6bab29de..8c0c524dd232 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -401,6 +401,24 @@
  *	@inode contains a pointer to the inode.
  *	@secid contains a pointer to the location where result will be saved.
  *	In case of failure, @secid will be set to zero.
+ * @inode_copy_up:
+ *	Appropriately label the destination inode when a unioned file is copied
+ *	up from a lower layer to the union/overlay layer.
+ *	@src indicates the file that is being copied up.
+ *	@dst indicates the file that has being created by the copy up.
+ *	Returns 0 on success or a negative error code on error.
+ * @inode_copy_up_xattr:
+ *	Filter/modify the xattrs being copied up when a unioned file is copied
+ *	up from a lower layer to the union/overlay layer.
+ *	@src indicates the file that is being copied up.
+ *	@dst indicates the file that has being created by the copy up.
+ *	@name indicates the name of the xattr.
+ *	@value, *@size indicate the payload of the xattr.
+ *	Returns 0 to accept the xattr, 1 to discard the xattr or a negative
+ *	error code to abort the copy up.  The xattr buffer must be at least
+ *	XATTR_SIZE_MAX in capacity and the contents may be modified and *@size
+ *	changed appropriately.  Note that the caller is responsible for reading
+ *	and writing the xattrs as this hook is merely a filter.
  *
  * Security hooks for file operations
  *
@@ -1421,6 +1439,9 @@ union security_list_options {
 	int (*inode_listsecurity)(struct inode *inode, char *buffer,
 					size_t buffer_size);
 	void (*inode_getsecid)(const struct inode *inode, u32 *secid);
+	int (*inode_copy_up) (struct dentry *src, struct dentry *dst);
+	int (*inode_copy_up_xattr) (struct dentry *src, struct dentry *dst,
+				    const char *name, void *value, size_t *size);
 
 	int (*file_permission)(struct file *file, int mask);
 	int (*file_alloc_security)(struct file *file);
@@ -1689,6 +1710,8 @@ struct security_hook_heads {
 	struct list_head inode_setsecurity;
 	struct list_head inode_listsecurity;
 	struct list_head inode_getsecid;
+	struct list_head inode_copy_up;
+	struct list_head inode_copy_up_xattr;
 	struct list_head file_permission;
 	struct list_head file_alloc_security;
 	struct list_head file_free_security;
diff --git a/include/linux/security.h b/include/linux/security.h
index 2f4c1f7aa7db..ec21144d8807 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -274,6 +274,10 @@ int security_inode_getsecurity(const struct inode *inode, const char *name, void
 int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags);
 int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
 void security_inode_getsecid(const struct inode *inode, u32 *secid);
+int security_inode_copy_up(struct dentry *src, struct dentry *dst);
+int security_inode_copy_up_xattr(struct dentry *src, struct dentry *dst,
+				 const char *name, void *value, size_t *size);
+
 int security_file_permission(struct file *file, int mask);
 int security_file_alloc(struct file *file);
 void security_file_free(struct file *file);
@@ -739,6 +743,16 @@ static inline void security_inode_getsecid(const struct inode *inode, u32 *secid
 	*secid = 0;
 }
 
+static inline int security_inode_copy_up(struct dentry *src, struct dentry *dst)
+{
+	return 0;
+}
+static inline int security_inode_copy_up_xattr(struct dentry *src, struct dentry *dst,
+					       const char *name, const void *value, size_t *size)
+{
+	return 0;
+}
+
 static inline int security_file_permission(struct file *file, int mask)
 {
 	return 0;
diff --git a/security/security.c b/security/security.c
index 46f405ce6b0f..e33c5d5bdc6b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -726,6 +726,19 @@ void security_inode_getsecid(const struct inode *inode, u32 *secid)
 	call_void_hook(inode_getsecid, inode, secid);
 }
 
+int security_inode_copy_up(struct dentry *src, struct dentry *dst)
+{
+	return call_int_hook(inode_copy_up, 0, src, dst);
+}
+EXPORT_SYMBOL(security_inode_copy_up);
+
+int security_inode_copy_up_xattr(struct dentry *src, struct dentry *dst,
+				 const char *name, void *value, size_t *size)
+{
+	return call_int_hook(inode_copy_up_xattr, 0, src, dst, name, value, size);
+}
+EXPORT_SYMBOL(security_inode_copy_up_xattr);
+
 int security_file_permission(struct file *file, int mask)
 {
 	int ret;
@@ -1654,6 +1667,10 @@ struct security_hook_heads security_hook_heads = {
 		LIST_HEAD_INIT(security_hook_heads.inode_listsecurity),
 	.inode_getsecid =
 		LIST_HEAD_INIT(security_hook_heads.inode_getsecid),
+	.inode_copy_up =
+		LIST_HEAD_INIT(security_hook_heads.inode_copy_up),
+	.inode_copy_up_xattr =
+		LIST_HEAD_INIT(security_hook_heads.inode_copy_up_xattr),
 	.file_permission =
 		LIST_HEAD_INIT(security_hook_heads.file_permission),
 	.file_alloc_security =