Re: [PATCH v4 12/24] read-cache: read index-v5

[Antoine Pelisse <apelisse@gmail.com>]

On Wed, Nov 27, 2013 at 1:00 PM, Thomas Gummerer <t.gummerer@gmail.com> wrote:
> +static int verify_hdr(void *mmap, unsigned long size)
> +{
> +       uint32_t *filecrc;
> +       unsigned int header_size;
> +       struct cache_header *hdr;
> +       struct cache_header_v5 *hdr_v5;
> +
> +       if (size < sizeof(struct cache_header)
> +           + sizeof (struct cache_header_v5) + 4)
> +               die("index file smaller than expected");
> +
> +       hdr = mmap;
> +       hdr_v5 = ptr_add(mmap, sizeof(*hdr));
> +       /* Size of the header + the size of the extensionoffsets */
> +       header_size = sizeof(*hdr) + sizeof(*hdr_v5) + hdr_v5->hdr_nextension * 4;
> +       /* Initialize crc */
> +       filecrc = ptr_add(mmap, header_size);
> +       if (!check_crc32(0, hdr, header_size, ntohl(*filecrc)))
> +               return error("bad index file header crc signature");
> +       return 0;
> +}

I find it curious that we actually need a value from the header (and
use it for pointer arithmetic) to check that the header is valid. The
application will crash before the crc is checked if
hdr_v5->hdr_nextensions is corrupted. Or am I missing something ?