io_uring: clean up io_uring_register_get_file()

Make it always reference the returned file. It's safer, especially with
unregistrations happening under it. And it makes the api cleaner with no
conditional clean ups by the caller.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0d0b13a63e8edd6b5d360fc821dcdb035cb6b7e0.1736995897.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/register.c

@@ -853,6 +853,8 @@ struct file *io_uring_register_get_file(unsigned int fd, bool registered)
 			return ERR_PTR(-EINVAL);
 		fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
 		file = tctx->registered_rings[fd];
+		if (file)
+			get_file(file);
 	} else {
 		file = fget(fd);
 	}
@@ -919,7 +921,7 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
 	trace_io_uring_register(ctx, opcode, ctx->file_table.data.nr,
 				ctx->buf_table.nr, ret);
 	mutex_unlock(&ctx->uring_lock);
-	if (!use_registered_ring)
-		fput(file);
+
+	fput(file);
 	return ret;
 }

io_uring/rsrc.c

@@ -1079,7 +1079,6 @@ int io_register_clone_buffers(struct io_ring_ctx *ctx, void __user *arg)
 	if (src_ctx != ctx)
 		mutex_unlock(&src_ctx->uring_lock);
 
-	if (!registered_src)
-		fput(file);
+	fput(file);
 	return ret;
 }