Badname file content access

[DerDonut]

This proposal is the counterpart of the modifications from the -badname parameter. It modifies the plain -> cipher mapping for filenames when using -badname parameter. The new function EncryptAndHashBadName tries to find a cipher filename for the given plain name with the following steps:

1. If badname is disabled or direct mapping is successful: Map directly (default and current behaviour)
2. If a file with badname flag has a valid cipher file, this is returned (=File just ends with the badname flag)
3. If a file with a badname flag exists where only the badname flag was added, this is returned (=File cipher name could not be decrypted by function DecryptName and just the badname flag was added)
4. Search for all files which cipher file name extists when cropping more and more characters from the end. If only 1 file is found, return this
5. Return an error otherwise

This allows file access in the file browsers but most important it allows that you rename files with undecryptable cipher names in the plain directories. Renaming those files will then generate a proper cipher filename
One backdraft: When mounting the cipher dir with -badname parameter, you can never create (or rename to) files whose file name ends with the badname file flag (at the moment this is " GOCRYPTFS_BAD_NAME"). This will cause an error.

I modified the CLI test function to cover additional test cases. Test Case 7 cannot be performed since the cli tests are executed in panic mode. The testing is stopped on error. Since the functionDecryptName produces internal errors when hitting non-decryptable file names, this test was omitted.

This implementation is a proposal where I tried to change the minimum amount of existing code. Another possibility would be instead of creating the new function EncryptAndHashBadName to modify the signature of the existing function EncryptAndHashName(name string, iv []byte) to EncryptAndHashName(name string, iv []byte, dirfd int) and integrate the functionality into this function directly. You may allow calling with dirfd=-1 or other invalid values an then performing the current functionality.

[rfjakob]

Hi, thanks! Before I review the code in detail, the git situation is a little complicated because you have merges inside your pull request. Can you:

1. Merge with latest master (I checked and it merges without conflicts, then there is one small change needed (build error) because EncryptName now returns an error value).

2. Squash all changes to a single commit ( here is how to do it without re-doing all the merges: https://stackoverflow.com/a/67041865/1380267 )

One code comment already:

3. In TestBadname, enable the "Case 7" test by setting wpanic=0 like done here:
   

   gocryptfs/tests/cli/cli_test.go

   Line 402 in 98ab59c

   func TestMountPasswordIncorrect(t *testing.T) {

[rfjakob]

4. Add EncryptAndHashBadName to the NameTransformer interface so you can remove all rn.nameTransform.(*nametransform.NameTransform) type assertions

[DerDonut]

Hi, thanks! Before I review the code in detail, the git situation is a little complicated because you have merges inside your pull request.

Yeah sorry about that. I messed up my master branch since I accidentally committed on that branch.
I now merged your master into mine and into badnamecontent. I also created the branch bnc-squashed as described there, is that how you meant it? Did I get this correctly that I have to create another pull request with that branch?

1. Add `EncryptAndHashBadName`  to the NameTransformer interface so you can remove all `rn.nameTransform.(*nametransform.NameTransform)` type assertions

I'm not quite sure if I get what you mean. EncryptAndHashBadName is already in that interface. The assertions (e.g. in node_helpers.go#L124) are used to get the parameter configuration. Is there a better way to do it?

3. In TestBadname, enable the "Case 7" test by setting wpanic=0 like done here:

I edited the CLI test. Thanks for the hint - I was searching for that.

[rfjakob]

Hmm, the merged commit doesn't look good: 1,298 additions and 279 deletions. Did you maybe do step (1) and (2) in reverse order?

I did this:

$ git checkout DerDonut-badnamecontent
Switched to branch 'DerDonut-badnamecontent'

$ git merge master

$ git diff master > squashed.patch

$ git checkout master -b pull568-squashed

$ patch -p1 < squashed.patch

$ git commit -av

and the result is here: https://github.com/rfjakob/gocryptfs/tree/pull568-squashed

Anyway, no need to redo this, you can just continue on pull568-squashed.

You can then create a new pull request, or (preferred), force-push into your badnamecontent branch, which will update this pull request.

[rfjakob]

About the EncryptAndHashBadName interface, sorry, my mistake, wrong function.
I meant to add HaveBadnamePatterns to the interface, which returns true if len(ntransform.BadnamePatterns) > 0.

[DerDonut]

Phew! I think that's it. Can you check the current badnamecontent branch? The first commit from me there now has 205 additions and 27 deletions.
Thank you for your patience. I am still getting into the git system.

[rfjakob]

Merged as a611810 , thanks!