Re: Fwd: New Defects reported by Coverity Scan for git

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 18, 2017, 17:23 UTC
Message-ID: <xmqqa841fylf.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <CAGZ79kaPFDMn2K0f529-Crzv+vhU3XUMsSM6w3QV4RXKBv5s_g@mail.gmail.com>

Stefan Beller <sbeller@google.com> writes:

Show 11 quoted lines

> I looked at this report for a while. My current understanding:
> * its detection was triggered by including rs/move-array,
>   f331ab9d4c (use MOVE_ARRAY, 2017-07-15)
> * But it is harmless, because the scan logic does not understand
>   how ALLOC_GROW works. It assumes that
>   done_pbase_paths_alloc can be larger
>   than done_pbase_paths_num + 1, while done_pbase_paths
>   is NULL, such that the memory allocation is not triggered.
>   If that were the case, then we have 2 subsequent dereferences
>   of a NULL pointer right after that. But by inspecting the use
>   of _alloc and _num the initial assumption does not seem possible.

Yes, it does appear that way. ALLOC_GROW() calls REALLOC_ARRAY() which safely can realloc NULL to specified size via xrealloc().

I'd be more worried about segfault we seem to be getting only on Windows from this:

    git -C parent grep -e "(1|2)d(3|4)" --recurse-submodules HEAD^ > actual

in https://travis-ci.org/git/git/jobs/254654195 by the way.