[Libguestfs] [PATCH v2 1/2] lib: change how hbin sections are read.
Richard W.M. Jones
rjones at redhat.com
Wed Feb 15 16:54:21 UTC 2017
On Tue, Feb 14, 2017 at 12:05:20PM -0500, Dawid Zamirski wrote:
> * hivex_open: when looping over hbin sections (aka pages), handle a
> case where following hbin section may not begin at exactly at the end
> of previous one. If this happens, scan the page section until next
> one is found and validate it by checking declared offset with actual
> one - if they match, all is good and we can safely move on.
>
> Rationale: there are registry hives there is some garbage data between
> hbin section but the hive is still perfectly usable as long as the
> offsets stated in hbin headers are correct.
> ---
> lib/handle.c | 39 ++++++++++++++++++++++++++++++++++-----
> 1 file changed, 34 insertions(+), 5 deletions(-)
>
> diff --git a/lib/handle.c b/lib/handle.c
> index 4565d7d..e183ff2 100644
> --- a/lib/handle.c
> +++ b/lib/handle.c
> @@ -226,11 +226,30 @@ hivex_open (const char *filename, int flags)
> page->magic[1] != 'b' ||
> page->magic[2] != 'i' ||
> page->magic[3] != 'n') {
> - SET_ERRNO (ENOTSUP,
> - "%s: trailing garbage at end of file "
> - "(at 0x%zx, after %zu pages)",
> - filename, off, pages);
> - goto error;
> +
> + DEBUG (2,
> + "page not found at expected offset 0x%zx, "
> + "seeking until one is found or EOF is reached",
> + off);
> +
> + int found = 0;
> + while (off < h->endpages) {
GCC 7 warns:
handle.c: In function 'hivex_open':
handle.c:236:13: error: missed loop optimization, the loop counter may overflow [-Werror=unsafe-loop-optimizations]
while (off < h->endpages) {
^
I suspect this means that GCC might try to turn this into an infinite
loop.
There are actually a few more of these in the existing code - I'm
going to push a patch to fix these in a minute.
Rich.
> + off += 0x1000;
> + page = (struct ntreg_hbin_page *) ((char *) h->addr + off);
> + if (page->magic[0] == 'h' &&
> + page->magic[1] == 'b' &&
> + page->magic[2] == 'i' &&
> + page->magic[3] == 'n') {
> + DEBUG (2, "found next page by seeking at 0x%zx", off);
> + found = 1;
> + break;
> + }
> + }
> +
> + if (!found) {
> + DEBUG (2, "page not found and end of pages section reached");
> + break;
> + }
> }
>
> size_t page_size = le32toh (page->page_size);
> @@ -254,6 +273,16 @@ hivex_open (const char *filename, int flags)
> goto error;
> }
>
> + size_t page_offset = le32toh(page->offset_first) + 0x1000;
> +
> + if (page_offset != off) {
> + SET_ERRNO (ENOTSUP,
> + "%s: declared page offset (0x%zx) does not match computed "
> + "offset (0x%zx), bad registry",
> + filename, page_offset, off);
> + goto error;
> + }
> +
> /* Read the blocks in this page. */
> size_t blkoff;
> struct ntreg_hbin_block *block;
> --
> 2.9.3
>
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--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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