A FUSE file system mounted without allow_other, such as a GVfs share,
denies root access to files that its owner can open. Mounting a volume
stored there, or formatting a new one with a non-FAT file system, failed
with "Permission denied".
When root is denied opening an existing volume file, re-execute
VeraCrypt with the internal option --requester-helper. The helper
permanently takes the credentials of the user who requested elevation
through sudo or doas, opens the file and passes the descriptor back.
Root does all I/O through that descriptor and mounts the volume through
the FUSE volume image. Another helper restores the timestamps when the
FUSE service closes the file.
This also lets volumes on NFS with root_squash mount read-write instead
of falling back to read-only.
Fixes#23
Mounir IDRASSI
eb9d10f430