Subject: Re: [ JGIT ] incompatiblity found in DirCache

From: "Shawn O. Pearce" <[email-masked]>
Date: Fri, 11 Sep 2009 08:05:23 -0700

Robin Rosenberg <[email-masked]> wrote:
> onsdag 09 september 2009 20:55:39 skrev "Adam W. Hawks" <[email-masked]>:
> > When using the DirCache interface to the index you can create a
> > invalid/corrupt tree for git 1.6.5.
> > 
> > The problem seems to be you can add a path to the index that starts
> > with a "/" and DirCache creates a entry with a mode but no path.
> > This causes git 1.6.5 to fail with a corrupt tree.
> 
> I think there are more ways of entering bad stuff. Preventing a
> deliberate programmatic creation of invalid trees is probably not
> the most important thing, but then again, validating the data to
> prevent e.g. the EGit plugin from doing it by mistake due to bugs
> could probably be worthwhile.

We already check for and fail fast on a 0 mode in DirCache, as this
mode is also not valid in the index, or in a git tree.

We should be doing the same thing for an empty path name.  "a//b" is
not a valid path in the index, as "" is not a valid tree entry path.
For the same reason, "/a" is not a valid path in the index.

Unfortunately our API also allows you to try and create a name of
"a\u0000b", which is a valid Java string, but will create a corrupt
tree.  \u0000 in a name with more than 4095 bytes will also create
a corrupt index (shorter strings are semi-valid because shorter
strings use a Pascal like string format, and longer ones use a C
like string format).  Though C git is unable to access a path whose
name contains "\u0000", no matter how long the string is.

I think we should try a bit harder in DirCache to prevent these sorts
of really bad entries from being constructed by application code.
Yes, applications should not do this, but I think the library also
should not write known bogus trash to the disk and claim it is OK.

I'll try to work up a patch for this today.

-- 
Shawn.