loading filesystem tree: location out of bounds.

[josch]

Steps to reproduce:

$ mkdir foo
$ touch foo/bar
$ tar -C ./foo -c . > out.tar
$ tar tf out.tar
./
./bar
$ tar2sqfs rootfs.sqfs < out.tar
[...]
$ sqfs2tar rootfs.sqfs > out.tar
rootfs.sqfs: loading filesystem tree: location out of bounds.

[AgentD]

The problem is two fold:

• tar2sqfs sanitizes the path names, i.e. it turns ./bar into bar but turns ./ into an empty string.
• libsquashfs does not check and happily tries to add an entry with an empty string.
  • The SquashFS format stores directory entries with the length count off-by-one, assuming that zero length strings don't occour.
  • The resulting length libsquashfs stores is interpreted as a huge number by the reader.
  • The libsquashfs reader catches this when and sqfs2tar fails.

My proposed solution for this is as follows:

• Add a check to tar2sqfs that skips entries if the sanitized name is empty string
  • Issue a warning for this or abort unless it is a directory named ./
  • TODO: Add a new flag in a future version to use the permissions, etc... from ./ for the root node? Perhaps a more generic handle "cut off prefix X and turn X into the root node"?
• Add a check to sqfs_dir_writer_add_entry to throw an error if an empty string as supplied as an entry name.

Which is implemented by commits 018e0e0a8e3c36a6bedf60eedeb8262311d90869 and 063f57dec14986d1895d83d9113fd1dec7f135f4.