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()
  ...

1 files changed, 26 insertions, 31 deletions

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 83d9466710d6..56e811f9e5fa 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -892,15 +892,35 @@ static int prepare_open(struct dentry *dentry, int oflag, int ro,
 	return inode_permission(&nop_mnt_idmap, d_inode(dentry), acc);
 }
 
+static struct file *mqueue_file_open(struct filename *name,
+				     struct vfsmount *mnt, int oflag, bool ro,
+				     umode_t mode, struct mq_attr *attr)
+{
+	struct dentry *dentry;
+	struct file *file;
+	int ret;
+
+	dentry = start_creating_noperm(mnt->mnt_root, &QSTR(name->name));
+	if (IS_ERR(dentry))
+		return ERR_CAST(dentry);
+
+	ret = prepare_open(dentry, oflag, ro, mode, name, attr);
+	file = ERR_PTR(ret);
+	if (!ret) {
+		const struct path path = { .mnt = mnt, .dentry = dentry };
+		file = dentry_open(&path, oflag, current_cred());
+	}
+
+	end_creating(dentry);
+	return file;
+}
+
 static int do_mq_open(const char __user *u_name, int oflag, umode_t mode,
 		      struct mq_attr *attr)
 {
+	struct filename *name __free(putname) = NULL;;
 	struct vfsmount *mnt = current->nsproxy->ipc_ns->mq_mnt;
-	struct dentry *root = mnt->mnt_root;
-	struct filename *name;
-	struct path path;
-	int fd, error;
-	int ro;
+	int fd, ro;
 
 	audit_mq_open(oflag, mode, attr);
 
@@ -908,35 +928,10 @@ static int do_mq_open(const char __user *u_name, int oflag, umode_t mode,
 	if (IS_ERR(name))
 		return PTR_ERR(name);
 
-	fd = get_unused_fd_flags(O_CLOEXEC);
-	if (fd < 0)
-		goto out_putname;
-
 	ro = mnt_want_write(mnt);	/* we'll drop it in any case */
-	path.dentry = start_creating_noperm(root, &QSTR(name->name));
-	if (IS_ERR(path.dentry)) {
-		error = PTR_ERR(path.dentry);
-		goto out_putfd;
-	}
-	path.mnt = mnt;
-	error = prepare_open(path.dentry, oflag, ro, mode, name, attr);
-	if (!error) {
-		struct file *file = dentry_open(&path, oflag, current_cred());
-		if (!IS_ERR(file))
-			fd_install(fd, file);
-		else
-			error = PTR_ERR(file);
-	}
-out_putfd:
-	if (error) {
-		put_unused_fd(fd);
-		fd = error;
-	}
-	end_creating(path.dentry);
+	fd = FD_ADD(O_CLOEXEC, mqueue_file_open(name, mnt, oflag, ro, mode, attr));
 	if (!ro)
 		mnt_drop_write(mnt);
-out_putname:
-	putname(name);
 	return fd;
 }