Handling of filesystem driver issues caused by malicious filesystem images

General advise for dealing with filesystem images

Maliciously corrupted filesystem images are a rather broad attack vector for the Linux kernel because of the sheer size and complexity of the parsed data structures. When such a maliciously corrupted image is mounted by the kernel, it can exploit missing consistency checks in the filesystem driver and cause issues ranging from denial of service to full machine control. What makes such attacks difficult for the attacker (and thus relatively low severity) is that they require the system administrator to mount the malicious image - either by explicitly issuing the mount command or, for example, by plugging in an USB stick with the image and having enabled removable media automounting feature. 

Developers of actively maintained filesystems are taking care to strengthen the consistency checks in the filesystem driver code and fix reported issues in handling of corrupted filesystem images and SUSE is committed to deliver these fixes to our customers. However for old and unmaintained filesystems such as reiserfs or hfs, there is no upstream interest in and manpower for dealing with those issues. Thus possible reported CVE issues due to handling of corrupted filesystem images can stay unfixed for a long time or even forever.

As a general precaution we advise users not to mount filesystems from untrusted sources. If there is a need to access untrusted filesystem image, there is an option to access the filesystem image using FUSE filesystem driver (e.g. using grub2-mount utility) where the filesystem image is parsed by the userspace daemon which is much easier to securely contain and thus limit the impact of potential security vulnerabilities.