It is still possible for malware to infect your host system, if you transfer infected files directly between the guest and host operating systems or use shared folders.
Most of the malware is made to attack Windows operating system users and even if you transfer files between the host and guest you may still be safe to some extent. Windows malware can't do any harm to Linux as they have different kernels.
However, if the malware developer intentionally made the malware in a way that it can penetrate Linux operating system as well then it might work if the Host allows file transfer from guest to host and host to guest.
In most scenarios, one can be safe with a virtual machine than by duel booting Windows and Linux. In the later case the malware developer has complete control over the file-system and he can do anything he likes with the files that are present in the compromised system.