Re: [Qemu-devel] [PATCH] Correctly free nd structure

[Glauber Costa]

On Fri, Sep 18, 2009 at 01:17:29PM +0100, Mark McLoughlin wrote:
> On Thu, 2009-09-17 at 16:53 -0400, Glauber Costa wrote:
> > When we "free" a NICInfo structure, we can leak pointers, since we don't do
> > much more than setting used = 0.
> > 
> > We free() the model parameter, but we don't set it to NULL. This means that
> > a new user of this structure will see garbage in there. It was not noticed
> > before because reusing a NICInfo is not that common, but it can be, for
> > users of device pci hotplug.
> > 
> > A user hit it, described at 
> > https://bugzilla.redhat.com/show_bug.cgi?id=524022
> > 
> > This patch memset's the whole structure, guaranteeing that anyone reusing it
> > will see a fresh NICinfo. Also, we free some other strings that are 
> > currently
> > leaking.
> > 
> > This codebase is quite old, so this patch should feed all stable trees.
> > 
> > Signed-off-by: Glauber Costa <address@hidden>
> > ---
> >  net.c |    9 +++++++--
> >  1 files changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net.c b/net.c
> > index 340177e..a405895 100644
> > --- a/net.c
> > +++ b/net.c
> > @@ -2804,8 +2804,13 @@ void net_client_uninit(NICInfo *nd)
> >  {
> >      nd->vlan->nb_guest_devs--;
> >      nb_nics--;
> > -    nd->used = 0;
> > -    free((void *)nd->model);
> > +
> > +    qemu_free((void *)nd->model);
> > +    qemu_free((void *)nd->name);
> > +    qemu_free((void *)nd->devaddr);
> > +    qemu_free((void *)nd->id);
> > +
> > +    memset(nd, 0, sizeof(*nd));
> >  }
> >  
> 
> Looks good to me; my patch to port to QemuOpts actually zeros out the
> struct during init()
> 
> What is the (void *) cast for, though?
1) it was already there.
2) those strings are marked as const, gcc whins if you remove the void cast.