fs: port ->get_acl() 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 <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Christian Brauner (Microsoft) <[e-mail]>

Documentation/filesystems/locking.rst

···
 	int (*fileattr_set)(struct user_namespace *mnt_userns,
 			    struct dentry *dentry, struct fileattr *fa);
 	int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa);
-	struct posix_acl * (*get_acl)(struct user_namespace *, struct dentry *, int);
+	struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int);
 
 locking rules:
 	all may block

Documentation/filesystems/vfs.rst

···
 		int (*atomic_open)(struct inode *, struct dentry *, struct file *,
 				   unsigned open_flag, umode_t create_mode);
 		int (*tmpfile) (struct mnt_idmap *, struct inode *, struct file *, umode_t);
-		struct posix_acl * (*get_acl)(struct user_namespace *, struct dentry *, int);
+		struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int);
 	        int (*set_acl)(struct user_namespace *, struct dentry *, struct posix_acl *, int);
 		int (*fileattr_set)(struct user_namespace *mnt_userns,
 				    struct dentry *dentry, struct fileattr *fa);

fs/9p/acl.c

···
 
 }
 
-struct posix_acl *v9fs_iop_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *v9fs_iop_get_acl(struct mnt_idmap *idmap,
 				   struct dentry *dentry, int type)
 {
 	struct v9fs_session_info *v9ses;

fs/9p/acl.h

···
 int v9fs_get_acl(struct inode *inode, struct p9_fid *fid);
 struct posix_acl *v9fs_iop_get_inode_acl(struct inode *inode, int type,
 				   bool rcu);
-struct posix_acl *v9fs_iop_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *v9fs_iop_get_acl(struct mnt_idmap *idmap,
 					  struct dentry *dentry, int type);
 int v9fs_iop_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		     struct posix_acl *acl, int type);

fs/cifs/cifsacl.c

···
 	return rc;
 }
 
-struct posix_acl *cifs_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *cifs_get_acl(struct mnt_idmap *idmap,
 			       struct dentry *dentry, int type)
 {
 #if defined(CONFIG_CIFS_ALLOW_INSECURE_LEGACY) && defined(CONFIG_CIFS_POSIX)

fs/cifs/cifsproto.h

···
 				      const char *, u32 *, u32);
 extern struct cifs_ntsd *get_cifs_acl_by_fid(struct cifs_sb_info *,
 				const struct cifs_fid *, u32 *, u32);
-extern struct posix_acl *cifs_get_acl(struct user_namespace *mnt_userns,
+extern struct posix_acl *cifs_get_acl(struct mnt_idmap *idmap,
 				      struct dentry *dentry, int type);
 extern int cifs_set_acl(struct user_namespace *mnt_userns,
 			struct dentry *dentry, struct posix_acl *acl, int type);

fs/ecryptfs/inode.c

···
 	return rc;
 }
 
-static struct posix_acl *ecryptfs_get_acl(struct user_namespace *mnt_userns,
+static struct posix_acl *ecryptfs_get_acl(struct mnt_idmap *idmap,
 					  struct dentry *dentry, int type)
 {
-	return vfs_get_acl(mnt_userns, ecryptfs_dentry_to_lower(dentry),
+	return vfs_get_acl(idmap, ecryptfs_dentry_to_lower(dentry),
 			   posix_acl_xattr_name(type));
 }
 

fs/overlayfs/inode.c

···
 {
 	struct posix_acl *real_acl, *clone;
 	struct user_namespace *mnt_userns;
+	struct mnt_idmap *idmap;
 	struct inode *realinode = d_inode(path->dentry);
 
-	mnt_userns = mnt_user_ns(path->mnt);
+	idmap = mnt_idmap(path->mnt);
+	mnt_userns = mnt_idmap_owner(idmap);
 
 	if (noperm)
 		real_acl = get_inode_acl(realinode, posix_acl_type(acl_name));
 	else
-		real_acl = vfs_get_acl(mnt_userns, path->dentry, acl_name);
+		real_acl = vfs_get_acl(idmap, path->dentry, acl_name);
 	if (IS_ERR_OR_NULL(real_acl))
 		return real_acl;
 
···
  *
  * This is obviously only relevant when idmapped layers are used.
  */
-struct posix_acl *do_ovl_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap,
 				 struct inode *inode, int type,
 				 bool rcu, bool noperm)
 {
···
 
 		ovl_path_lower(dentry, &realpath);
 		old_cred = ovl_override_creds(dentry->d_sb);
-		real_acl = vfs_get_acl(mnt_user_ns(realpath.mnt), realdentry,
+		real_acl = vfs_get_acl(mnt_idmap(realpath.mnt), realdentry,
 				       acl_name);
 		revert_creds(old_cred);
 		if (IS_ERR(real_acl)) {

fs/overlayfs/overlayfs.h

···
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
 
 #ifdef CONFIG_FS_POSIX_ACL
-struct posix_acl *do_ovl_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *do_ovl_get_acl(struct mnt_idmap *idmap,
 				 struct inode *inode, int type,
 				 bool rcu, bool noperm);
 static inline struct posix_acl *ovl_get_inode_acl(struct inode *inode, int type,
 						  bool rcu)
 {
-	return do_ovl_get_acl(&init_user_ns, inode, type, rcu, true);
+	return do_ovl_get_acl(&nop_mnt_idmap, inode, type, rcu, true);
 }
-static inline struct posix_acl *ovl_get_acl(struct user_namespace *mnt_userns,
+static inline struct posix_acl *ovl_get_acl(struct mnt_idmap *idmap,
 					    struct dentry *dentry, int type)
 {
-	return do_ovl_get_acl(mnt_userns, d_inode(dentry), type, false, false);
+	return do_ovl_get_acl(idmap, d_inode(dentry), type, false, false);
 }
 int ovl_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		struct posix_acl *acl, int type);

fs/posix_acl.c

···
 }
 EXPORT_SYMBOL(forget_all_cached_acls);
 
-static struct posix_acl *__get_acl(struct user_namespace *mnt_userns,
+static struct posix_acl *__get_acl(struct mnt_idmap *idmap,
 				   struct dentry *dentry, struct inode *inode,
 				   int type)
 {
···
 	 * we'll just create the negative cache entry.
 	 */
 	if (dentry && inode->i_op->get_acl) {
-		acl = inode->i_op->get_acl(mnt_userns, dentry, type);
+		acl = inode->i_op->get_acl(idmap, dentry, type);
 	} else if (inode->i_op->get_inode_acl) {
 		acl = inode->i_op->get_inode_acl(inode, type, false);
 	} else {
···
 
 struct posix_acl *get_inode_acl(struct inode *inode, int type)
 {
-	return __get_acl(&init_user_ns, NULL, inode, type);
+	return __get_acl(&nop_mnt_idmap, NULL, inode, type);
 }
 EXPORT_SYMBOL(get_inode_acl);
 
···
 
 /**
  * vfs_get_acl - get posix acls
- * @mnt_userns: user namespace of the mount
+ * @idmap: idmap of the mount
  * @dentry: the dentry based on which to retrieve the posix acls
  * @acl_name: the name of the posix acl
  *
···
  *
  * Return: On success POSIX ACLs in VFS format, on error negative errno.
  */
-struct posix_acl *vfs_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *vfs_get_acl(struct mnt_idmap *idmap,
 			      struct dentry *dentry, const char *acl_name)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	struct inode *inode = d_inode(dentry);
 	struct posix_acl *acl;
 	int acl_type, error;
···
 	if (S_ISLNK(inode->i_mode))
 		return ERR_PTR(-EOPNOTSUPP);
 
-	acl = __get_acl(mnt_userns, dentry, inode, acl_type);
+	acl = __get_acl(idmap, dentry, inode, acl_type);
 	if (IS_ERR(acl))
 		return acl;
 	if (!acl)
···
 	ssize_t error;
 	struct posix_acl *acl;
 
-	acl = vfs_get_acl(mnt_idmap_owner(idmap), dentry, acl_name);
+	acl = vfs_get_acl(idmap, dentry, acl_name);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);
 

include/linux/fs.h

···
 			   umode_t create_mode);
 	int (*tmpfile) (struct mnt_idmap *, struct inode *,
 			struct file *, umode_t);
-	struct posix_acl *(*get_acl)(struct user_namespace *, struct dentry *,
+	struct posix_acl *(*get_acl)(struct mnt_idmap *, struct dentry *,
 				     int);
 	int (*set_acl)(struct user_namespace *, struct dentry *,
 		       struct posix_acl *, int);

include/linux/posix_acl.h

···
 
 int vfs_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		const char *acl_name, struct posix_acl *kacl);
-struct posix_acl *vfs_get_acl(struct user_namespace *mnt_userns,
+struct posix_acl *vfs_get_acl(struct mnt_idmap *idmap,
 			      struct dentry *dentry, const char *acl_name);
 int vfs_remove_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
 		   const char *acl_name);
···
 	return -EOPNOTSUPP;
 }
 
-static inline struct posix_acl *vfs_get_acl(struct user_namespace *mnt_userns,
+static inline struct posix_acl *vfs_get_acl(struct mnt_idmap *idmap,
 					    struct dentry *dentry,
 					    const char *acl_name)
 {