Re: [PATCH] attr.c: move ATTR_MAX_FILE_SIZE check into read_attr_from_buf()

> Commit 3c50032ff52 (attr: ignore overly large gitattributes files,
> 2022-12-01) added a defense-in-depth check to ensure that .gitattributes
> blobs read from the index do not exceed ATTR_MAX_FILE_SIZE (100 MB).
> 
> But there were two cases added shortly after 3c50032ff52 was written
> which do not apply similar protections:
> 
>   - 47cfc9bd7d0 (attr: add flag `--source` to work with tree-ish,
>     2023-01-14)
> 
>   - 4723ae1007f (attr.c: read attributes in a sparse directory,
>     2023-08-11) added a similar
> 
> Ensure that we refuse to process a .gitattributes blob exceeding
> ATTR_MAX_FILE_SIZE when reading from either an arbitrary tree object or
> a sparse directory. This is done by pushing the ATTR_MAX_FILE_SIZE check
> down into the low-level `read_attr_from_buf()`.
> 
> In doing so, plug a leak in `read_attr_from_index()` where we would
> accidentally leak the large buffer upon detecting it is too large to
> process.
> 
> (Since `read_attr_from_buf()` handles a NULL buffer input, we can remove
> a NULL check before calling it in `read_attr_from_index()` as well).
> 
> Co-authored-by: Jeff King <peff@peff.net>
> Signed-off-by: Jeff King <peff@peff.net>
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---