import-tar: the dotslash issue

[ThomasWaldmann]

User JyZyXy (from #borgbackup IRC) exported tar files from the backuppc software and all the paths archived in these tars start with ./, e.g. ./somedir/somefile (because that software does it that way and can't be easily configured to leave away the ./).

Then they imported these tars into borg, using borg import-tar.

After that, they noticed that they can do a full extraction using borg extract, but borg mount didn't show anything.

borgbackup 1.4.0

[ThomasWaldmann]

When using borg create, the paths in the archive are always "normalized":

• they start with the recursion root
• they are normalized, they never have ./ at the beginning
• they are relativized, they never have / at the beginning
• they are made safe, they never have ../ at the beginning

borg import-tar missed these normalization / make safe steps, so it produced archived paths that borg mount could not correctly process, thus the mounted fs was empty.

[ThomasWaldmann]

Fixed by:

• 1.2-maint: import-tar: fix the dotslash issue, add test #8942 and import-tar: when printing the path, use the already normalized item.path.  #8946
• 1.4-maint: import-tar dotslash issue (1.4-maint) #8941 and import-tar: when printing the path, use the already normalized item.path. #8945
• master: import-tar: fix the dotslash issue, add test #8943 and import-tar: normalize and sanitize tarinfo.linkname (master) #8944

[ThomasWaldmann]

Side notes:

• tarinfo.linkname (link target for symlinks), must be archived as is, no normalization / no "make safe".

  A symlink is always extracted as a symlink and it is allowed to have broken symlinks, symlinks starting with ../ or ./. The symlink target has to be seen like regular file content: we archive what the user has, we restore what the user had - we must not change user content, we must not change symlink targets.

• master branch uses a hard link manager (hlm) that maintains a mapping paths -> list of content chunks. code was changed to use the archived item.path (which is normalized/safe) as key for the "remember" call and thus needed to use a normalized/safe path for the "retrieve" operation also.