From mboxrd@z Thu Jan  1 00:00:00 1970
From: Antoine Pelisse <apelisse@gmail.com>
Subject: Re: [PATCH v4 12/24] read-cache: read index-v5
Date: Sat, 30 Nov 2013 16:26:46 +0100
Message-ID: <CALWbr2xUMHSU0MV-6nVbN4_eSMoj3Eyc_Ta_CxTwZ_Y8tLfbdQ@mail.gmail.com>
References: <1385553659-9928-1-git-send-email-t.gummerer@gmail.com>
	<1385553659-9928-13-git-send-email-t.gummerer@gmail.com>
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Cc: git <git@vger.kernel.org>, Junio C Hamano <gitster@pobox.com>,
	Thomas Rast <tr@thomasrast.ch>,
	Michael Haggerty <mhagger@alum.mit.edu>,
	=?UTF-8?B?Tmd1eeG7hW4gVGjDoWkgTmfhu41jIER1eQ==?= 
	<pclouds@gmail.com>, robin.rosenberg@dewire.com,
	Eric Sunshine <sunshine@sunshineco.com>,
	ramsay@ramsay1.demon.co.uk
To: Thomas Gummerer <t.gummerer@gmail.com>
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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 ?