[PATCH RFC POC 23/50] file: open-code receive_fd()'s immediate install

[Christian Brauner]

receive_fd() cannot defer to syscall exit as SECCOMP_IOCTL_NOTIF_ADDFD
installs into the target task and hands the number to the supervisor
and IORING_OP_FIXED_FD_INSTALL runs from an io_uring op. Open-code the
get_unused_fd_flags() + fd_install() it did through FD_PREPARE().

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 fs/file.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 2b041b45f225..1f06d0c846c2 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1607,25 +1607,27 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
  */
 int receive_fd(struct file *file, int __user *ufd, unsigned int o_flags)
 {
-	int error;
+	int fd, error;
 
 	error = security_file_receive(file);
 	if (error)
 		return error;
 
-	FD_PREPARE(fdf, o_flags, file);
-	if (fdf.err)
-		return fdf.err;
-	get_file(file);
+	fd = get_unused_fd_flags(o_flags);
+	if (fd < 0)
+		return fd;
 
 	if (ufd) {
-		error = put_user(fd_prepare_fd(fdf), ufd);
-		if (error)
+		error = put_user(fd, ufd);
+		if (error) {
+			put_unused_fd(fd);
 			return error;
+		}
 	}
 
-	__receive_sock(fd_prepare_file(fdf));
-	return fd_publish(fdf);
+	__receive_sock(file);
+	fd_install(fd, get_file(file));
+	return fd;
 }
 EXPORT_SYMBOL_GPL(receive_fd);
 

-- 
2.53.0