fs: port ->setattr() to pass mnt_idmap

Convert to struct mnt_idmap.

Last cycle we merged the necessary infrastructure in
256c8aed2b42 ("fs: introduce dedicated idmap type for mounts").
This is just the conversion to struct mnt_idmap.

Currently we still pass around the plain namespace that was attached to a
mount. This is in general pretty convenient but it makes it easy to
conflate namespaces that are relevant on the filesystem with namespaces
that are relevent on the mount level. Especially for non-vfs developers
without detailed knowledge in this area this can be a potential source for
bugs.

Once the conversion to struct mnt_idmap is done all helpers down to the
really low-level helpers will take a struct mnt_idmap argument instead of
two namespace arguments. This way it becomes impossible to conflate the two
eliminating the possibility of any bugs. All of the vfs and all filesystems
only operate on struct mnt_idmap.

Acked-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

1 files changed, 17 insertions, 15 deletions

diff --git a/fs/attr.c b/fs/attr.c
index 023a3860568a..39d35621e57b 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -142,7 +142,7 @@ static bool chgrp_ok(struct user_namespace *mnt_userns,
 
 /**
  * setattr_prepare - check if attribute changes to a dentry are allowed
- * @mnt_userns:	user namespace of the mount the inode was found from
+ * @idmap:	idmap of the mount the inode was found from
  * @dentry:	dentry to check
  * @attr:	attributes to change
  *
@@ -152,18 +152,19 @@ static bool chgrp_ok(struct user_namespace *mnt_userns,
  * SGID bit from mode if user is not allowed to set it. Also file capabilities
  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
  *
- * If the inode has been found through an idmapped mount the user namespace of
- * the vfsmount must be passed through @mnt_userns. This function will then
- * take care to map the inode according to @mnt_userns before checking
+ * If the inode has been found through an idmapped mount the idmap of
+ * the vfsmount must be passed through @idmap. This function will then
+ * take care to map the inode according to @idmap before checking
  * permissions. On non-idmapped mounts or if permission checking is to be
- * performed on the raw inode simply passs init_user_ns.
+ * performed on the raw inode simply passs @nop_mnt_idmap.
  *
  * Should be called as the first thing in ->setattr implementations,
  * possibly after taking additional locks.
  */
-int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
+int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry,
 		    struct iattr *attr)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	struct inode *inode = d_inode(dentry);
 	unsigned int ia_valid = attr->ia_valid;
 
@@ -276,7 +277,7 @@ EXPORT_SYMBOL(inode_newsize_ok);
 
 /**
  * setattr_copy - copy simple metadata updates into the generic inode
- * @mnt_userns:	user namespace of the mount the inode was found from
+ * @idmap:	idmap of the mount the inode was found from
  * @inode:	the inode to be updated
  * @attr:	the new attributes
  *
@@ -289,19 +290,20 @@ EXPORT_SYMBOL(inode_newsize_ok);
  * Noticeably missing is inode size update, which is more complex
  * as it requires pagecache updates.
  *
- * If the inode has been found through an idmapped mount the user namespace of
- * the vfsmount must be passed through @mnt_userns. This function will then
- * take care to map the inode according to @mnt_userns before checking
+ * If the inode has been found through an idmapped mount the idmap of
+ * the vfsmount must be passed through @idmap. This function will then
+ * take care to map the inode according to @idmap before checking
  * permissions. On non-idmapped mounts or if permission checking is to be
- * performed on the raw inode simply passs init_user_ns.
+ * performed on the raw inode simply pass @nop_mnt_idmap.
  *
  * The inode is not marked as dirty after this operation. The rationale is
  * that for "simple" filesystems, the struct inode is the inode storage.
  * The caller is free to mark the inode dirty afterwards if needed.
  */
-void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode,
+void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
 		  const struct iattr *attr)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	unsigned int ia_valid = attr->ia_valid;
 
 	i_uid_update(mnt_userns, attr, inode);
@@ -472,7 +474,7 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
 	    !vfsgid_valid(i_gid_into_vfsgid(mnt_userns, inode)))
 		return -EOVERFLOW;
 
-	error = security_inode_setattr(mnt_userns, dentry, attr);
+	error = security_inode_setattr(idmap, dentry, attr);
 	if (error)
 		return error;
 	error = try_break_deleg(inode, delegated_inode);
@@ -480,9 +482,9 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
 		return error;
 
 	if (inode->i_op->setattr)
-		error = inode->i_op->setattr(mnt_userns, dentry, attr);
+		error = inode->i_op->setattr(idmap, dentry, attr);
 	else
-		error = simple_setattr(mnt_userns, dentry, attr);
+		error = simple_setattr(idmap, dentry, attr);
 
 	if (!error) {
 		fsnotify_change(dentry, ia_valid);