Merge tag 'vfs-6.19-rc1.fd_prepare.fs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull fd prepare updates from Christian Brauner:
 "This adds the FD_ADD() and FD_PREPARE() primitive. They simplify the
  common pattern of get_unused_fd_flags() + create file + fd_install()
  that is used extensively throughout the kernel and currently requires
  cumbersome cleanup paths.

  FD_ADD() - For simple cases where a file is installed immediately:

      fd = FD_ADD(O_CLOEXEC, vfio_device_open_file(device));
      if (fd < 0)
          vfio_device_put_registration(device);
      return fd;

  FD_PREPARE() - For cases requiring access to the fd or file, or
  additional work before publishing:

      FD_PREPARE(fdf, O_CLOEXEC, sync_file->file);
      if (fdf.err) {
          fput(sync_file->file);
          return fdf.err;
      }

      data.fence = fd_prepare_fd(fdf);
      if (copy_to_user((void __user *)arg, &data, sizeof(data)))
          return -EFAULT;

      return fd_publish(fdf);

  The primitives are centered around struct fd_prepare. FD_PREPARE()
  encapsulates all allocation and cleanup logic and must be followed by
  a call to fd_publish() which associates the fd with the file and
  installs it into the caller's fdtable. If fd_publish() isn't called,
  both are deallocated automatically. FD_ADD() is a shorthand that does
  fd_publish() immediately and never exposes the struct to the caller.

  I've implemented this in a way that it's compatible with the cleanup
  infrastructure while also being usable separately. IOW, it's centered
  around struct fd_prepare which is aliased to class_fd_prepare_t and so
  we can make use of all the basica guard infrastructure"

* tag 'vfs-6.19-rc1.fd_prepare.fs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (42 commits)
  io_uring: convert io_create_mock_file() to FD_PREPARE()
  file: convert replace_fd() to FD_PREPARE()
  vfio: convert vfio_group_ioctl_get_device_fd() to FD_ADD()
  tty: convert ptm_open_peer() to FD_ADD()
  ntsync: convert ntsync_obj_get_fd() to FD_PREPARE()
  media: convert media_request_alloc() to FD_PREPARE()
  hv: convert mshv_ioctl_create_partition() to FD_ADD()
  gpio: convert linehandle_create() to FD_PREPARE()
  pseries: port papr_rtas_setup_file_interface() to FD_ADD()
  pseries: convert papr_platform_dump_create_handle() to FD_ADD()
  spufs: convert spufs_gang_open() to FD_PREPARE()
  papr-hvpipe: convert papr_hvpipe_dev_create_handle() to FD_PREPARE()
  spufs: convert spufs_context_open() to FD_PREPARE()
  net/socket: convert __sys_accept4_file() to FD_ADD()
  net/socket: convert sock_map_fd() to FD_ADD()
  net/kcm: convert kcm_ioctl() to FD_PREPARE()
  net/handshake: convert handshake_nl_accept_doit() to FD_PREPARE()
  secretmem: convert memfd_secret() to FD_ADD()
  memfd: convert memfd_create() to FD_ADD()
  bpf: convert bpf_token_create() to FD_PREPARE()
  ...

2 files changed, 23 insertions, 53 deletions

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 6ac35430c573..eec60b57bd3d 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -634,37 +634,24 @@ release_prog:
 int bpf_iter_new_fd(struct bpf_link *link)
 {
 	struct bpf_iter_link *iter_link;
-	struct file *file;
 	unsigned int flags;
-	int err, fd;
+	int err;
 
 	if (link->ops != &bpf_iter_link_lops)
 		return -EINVAL;
 
 	flags = O_RDONLY | O_CLOEXEC;
-	fd = get_unused_fd_flags(flags);
-	if (fd < 0)
-		return fd;
-
-	file = anon_inode_getfile("bpf_iter", &bpf_iter_fops, NULL, flags);
-	if (IS_ERR(file)) {
-		err = PTR_ERR(file);
-		goto free_fd;
-	}
+
+	FD_PREPARE(fdf, flags, anon_inode_getfile("bpf_iter", &bpf_iter_fops, NULL, flags));
+	if (fdf.err)
+		return fdf.err;
 
 	iter_link = container_of(link, struct bpf_iter_link, link);
-	err = prepare_seq_file(file, iter_link);
+	err = prepare_seq_file(fd_prepare_file(fdf), iter_link);
 	if (err)
-		goto free_file;
+		return err; /* Automatic cleanup handles fput */
 
-	fd_install(fd, file);
-	return fd;
-
-free_file:
-	fput(file);
-free_fd:
-	put_unused_fd(fd);
-	return err;
+	return fd_publish(fdf);
 }
 
 struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop)
diff --git a/kernel/bpf/token.c b/kernel/bpf/token.c
index 0bbe412f854e..feecd8f4dbf9 100644
--- a/kernel/bpf/token.c
+++ b/kernel/bpf/token.c
@@ -110,16 +110,15 @@ const struct file_operations bpf_token_fops = {
 
 int bpf_token_create(union bpf_attr *attr)
 {
+	struct bpf_token *token __free(kfree) = NULL;
 	struct bpf_mount_opts *mnt_opts;
-	struct bpf_token *token = NULL;
 	struct user_namespace *userns;
 	struct inode *inode;
-	struct file *file;
 	CLASS(fd, f)(attr->token_create.bpffs_fd);
 	struct path path;
 	struct super_block *sb;
 	umode_t mode;
-	int err, fd;
+	int err;
 
 	if (fd_empty(f))
 		return -EBADF;
@@ -166,23 +165,20 @@ int bpf_token_create(union bpf_attr *attr)
 	inode->i_fop = &bpf_token_fops;
 	clear_nlink(inode); /* make sure it is unlinked */
 
-	file = alloc_file_pseudo(inode, path.mnt, BPF_TOKEN_INODE_NAME, O_RDWR, &bpf_token_fops);
-	if (IS_ERR(file)) {
-		iput(inode);
-		return PTR_ERR(file);
-	}
+	FD_PREPARE(fdf, O_CLOEXEC,
+		   alloc_file_pseudo(inode, path.mnt, BPF_TOKEN_INODE_NAME,
+				     O_RDWR, &bpf_token_fops));
+	if (fdf.err)
+		return fdf.err;
 
 	token = kzalloc(sizeof(*token), GFP_USER);
-	if (!token) {
-		err = -ENOMEM;
-		goto out_file;
-	}
+	if (!token)
+		return -ENOMEM;
 
 	atomic64_set(&token->refcnt, 1);
 
-	/* remember bpffs owning userns for future ns_capable() checks */
-	token->userns = get_user_ns(userns);
-
+	/* remember bpffs owning userns for future ns_capable() checks. */
+	token->userns = userns;
 	token->allowed_cmds = mnt_opts->delegate_cmds;
 	token->allowed_maps = mnt_opts->delegate_maps;
 	token->allowed_progs = mnt_opts->delegate_progs;
@@ -190,24 +186,11 @@ int bpf_token_create(union bpf_attr *attr)
 
 	err = security_bpf_token_create(token, attr, &path);
 	if (err)
-		goto out_token;
-
-	fd = get_unused_fd_flags(O_CLOEXEC);
-	if (fd < 0) {
-		err = fd;
-		goto out_token;
-	}
-
-	file->private_data = token;
-	fd_install(fd, file);
-
-	return fd;
+		return err;
 
-out_token:
-	bpf_token_free(token);
-out_file:
-	fput(file);
-	return err;
+	get_user_ns(token->userns);
+	fd_prepare_file(fdf)->private_data = no_free_ptr(token);
+	return fd_publish(fdf);
 }
 
 int bpf_token_get_info_by_fd(struct bpf_token *token,