[SOLVED] Tar: what's the implication of the ./ and ./file structure in the tar file? - eviltoast

Solved

After interesting/insightful inputs from different users, here are the takeaways:

  • It doesn’t have some critical or dangerous impact or implications when extracted
  • It contains the tared parent folder (see below for some neat tricks)
  • It only overwrites the owner/permission if ./ itself is included in the tar file as a directory.
  • Tarbombs are specially crafted tar archives with absolute paths / (by default (GNU) tar strips absolute paths and will throw a warning except if used with a special option –absolute-names or -P)
  • Interesting read: Path-traversal vulnerability (../)

Some neat trick I learned from the post

Temporarily created subshell with its own environment:

Let’s say you’re in the home directory that’s called /home/joe. You could go something like:

> (cd bin && pwd) && pwd
/home/joe/bin
/home/joe

source

Exclude parent folder and ./ ./file from tar

There are probably a lot of different ways to achieve that expected goal:

(cd mydir/ && tar -czvf mydir.tgz *)

find mydir/ -printf "%P\n" | tar -czf mytar.tgz --no-recursion -C mydir/ -T - source

The absolute path could overwrite my directory structure (tarbomb) source Will overwrite permission/owner to the current directory if extracted. source

I’m sorry if my question wasn’t clear enough, I’m really doing my best to be as comprehensible as possible :/

Hi everyone !

I’m playing a bit around with tar to understand how it works under the hood. While poking around and searching through the web I couldn’t find an actual answer, on what are the implication of ./ and ./file structure in the tar archive.

Output 1

sudo find ./testar -maxdepth 1 -type d,f -printf "%P\n" | sudo tar -czvf ./xtractar/tar1/testbackup1.tgz -C ./testar -T -

#output
> tar tf tar1/testbackup1.tgz 

text.tz
test
my
file.txt
.testzero
test01/
test01/never.xml
test01/file.exe
test01/file.tar
test01/files
test01/.testfiles
My test folder.txt

Output 2

sudo find ./testar -maxdepth 1 -type d,f  | sudo tar -czvf ./xtractar/tar2/testbackup2.tgz -C ./testar -T -

#output
>tar tf tar2/testbackup2.tgz

./testar/
./testar/text.tz
./testar/test
./testar/my
./testar/file.txt
./testar/.testzero
./testar/test01/
./testar/test01/never.xml
./testar/test01/file.exe
./testar/test01/file.tar
./testar/test01/files
./testar/test01/.testfiles
./testar/My test folder.txt
./testar/text.tz
./testar/test
./testar/my
./testar/file.txt
./testar/.testzero
./testar/test01/
./testar/test01/never.xml
./testar/test01/file.exe
./testar/test01/file.tar
./testar/test01/files
./testar/test01/.testfiles
./testar/My test folder.txt

The outputs are clearly different and if I extract them both the only difference I see is that the second outputs the parent folder. But reading here and here this is not a good solution? But nobody actually says why?

Has anyone a good explanation why the second way is bad practice? Or not recommended?

Thank you :)

  • eveninghere@beehaw.org
    1·
    8 months ago

    I don’t want:

    my_directory
   --- my_file
   --- my_file
   --- my_file

    I want:

    my_file
my_file
my_file

    Quoted from the question.

    • N0x0n@lemmy.mlOP
      1·
      8 months ago

      Yeah but that doesn’t answer my question: What’s the implication of ./ in the tar file? I mean when I extract them, both seem similar but most people say it’s bad practice or not recommended but why?

      I know and do understand how to achieve both with and without the root folder.

        • N0x0n@lemmy.mlOP
          1·
          8 months ago

          Thank you, I think this is a good lead, but couldn’t find a lot of information about it. But the general gist is that it could overwrite my folder structure and mess up the filesystem (source). All sources I found are very old, does that mean that there’s some kind of protection today?

          I also found out that it will extract the permission and owner to the current directory :/ so this a very odd behavior… (source).

          Thank you for your answer !

          • eveninghere@beehaw.org
            1·
            8 months ago

            I doubt there’s a perfect protection. Maybe some tar implementations asks confirmation before tar-bombing, but it then wouldn’t work for non-interactive sessions, etc.

            tar overwrites permissions because tar was meant for archiving iirc. Although, there might be a command line option to change its behavior.

            Perhaps, the zip command is better for your purpose. It doesn’t allow zip-bombs and perhaps doesn’t overwrite permission.