On Fri, Nov 13, 2020 at 04:29:54PM -0500, Taylor Blau wrote:
> > which is the header plus the trailer. We want to readjust for the
> > MAX_RAWSZ part of the header, so it should be:
> >
> > size_t header_size = sizeof(*header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz;
> > if (index->map_size < sizeof(*header) + the_hash_algo->rawsz)
>
> I'm not sure that I follow. If you apply this to the second patch in
> this series, the only thing that changes is that it factors out:
>
> index->map_pos += ...;
>
> into
>
> size_t header_size = ...;
> // ...
> index->map_pos += header_size;
>
> What am I missing here?
The problem is this hunk from patch 2:
> + size_t header_size = sizeof(*header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz;
>
> - if (index->map_size < sizeof(*header) + the_hash_algo->rawsz)
> + if (index->map_size < header_size)
> return error("Corrupted bitmap index (missing header data)");
The header struct contains a field for the hash of the pack. So the
original code as taking that full header, and adding in another
current-algo rawsz to account for the trailer.
Afterwards, we adjust header_size to swap out the MAX_RAWSZ for the
current-algo rawsz. So header_size is a correct substitution for
sizeof(*header) now. But we still have to add back in
the_hash_algo->rawsz to account for the trailer. The second "+" line is
wrong to have removed it.
The later line we adjust:
> - index->map_pos += sizeof(*header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz;
> + index->map_pos += header_size;
is correct. It's just skipping past the header, and doesn't care about
the trailer at all (and confusing the two is probably what led me to
write the bug in the first place).
-Peff
