Hello,

This is in the git sources release-4-0-0alpha7-2044-gecd1fe2,
but release-3-4-0pre2 has the same code.

I began looking through samba sources for unchecked close calls.
The one at the end of check_magic in source3/smbd/close.c looks significant:

	transfer_file(tmp_fd,outfd,(SMB_OFF_T)st.st_ex_size);
	close(tmp_fd);
	close(outfd);
	TALLOC_FREE(ctx);
}

The problem is that close(outfd) is documented to be able to fail (indicating a write failure) even when all "write" syscalls have succeeded, and that is not detected.