Re: [Libguestfs] [PATCH v2 1/2] lib: change how hbin sections are read.

On Wed, 2017-02-15 at 16:54 +0000, Richard W.M. Jones wrote: > 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. > I've just sent out v3 that fix this warning - it was a valid complaint from GCC7 because off += 0x1000; in the loop body is not a good idea anyway and it should have been off++;