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    SubjectRe: [syzbot] [hfs?] WARNING in hfs_write_inode
    Dmitry Vyukov <dvyukov@google.com> writes:

    > On Thu, 5 Jan 2023 at 17:45, Viacheslav Dubeyko <slava@dubeyko.com> wrote:
    >> > On Wed, Jan 04, 2023 at 08:37:16PM -0800, Viacheslav Dubeyko wrote:
    >> >> Also, as far as I can see, available volume in report (mount_0.gz) somehow corrupted already:
    >> >
    >> > Syzbot generates deliberately-corrupted (aka fuzzed) filesystem images.
    >> > So basically, you can't trust anything you read from the disc.
    >> >
    >>
    >> If the volume has been deliberately corrupted, then no guarantee that file system
    >> driver will behave nicely. Technically speaking, inode write operation should never
    >> happened for corrupted volume because the corruption should be detected during
    >> b-tree node initialization time. If we would like to achieve such nice state of HFS/HFS+
    >> drivers, then it requires a lot of refactoring/implementation efforts. I am not sure that
    >> it is worth to do because not so many guys really use HFS/HFS+ as the main file
    >> system under Linux.
    >
    >
    > Most popular distros will happily auto-mount HFS/HFS+ from anything
    > inserted into USB (e.g. what one may think is a charger). This creates
    > interesting security consequences for most Linux users.
    > An image may also be corrupted non-deliberately, which will lead to
    > random memory corruptions if the kernel trusts it blindly.

    I am going to point out that there are no known linux filesystems
    that are safe to mount when someone has written a deliberately
    corrupted filesystem on a usb stick.

    Some filesystems like ext4 make a best effort to fix bugs of this sort
    as they are discovered but unless something has changed since last I
    looked no one makes the effort to ensure that it is 100% safe to mount
    any possible corrupted version of any Linux filesystem.

    If there is any filesystem in Linux that is safe to automount from
    an untrusted USB stick I really would like to hear about it. We could
    allow mounting them in unprivileged user namespaces and give all kinds
    of interesting capabilities to our users.

    As it is I respectfully suggest that if there is a security issue it is
    the userspace code that automounts any filesystem on an untrusted USB
    stick.

    Eric




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