Re: [PULL 2/2] s390x/s390-virtio-ccw: fix loadparm property getter

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 28 Jul 2020 14:52:36 +0100
Peter Maydell <peter.maydell@linaro.org> wrote:

> On Mon, 27 Jul 2020 at 15:05, Cornelia Huck <cohuck@redhat.com> wrote:
> >
> > From: Halil Pasic <pasic@linux.ibm.com>
> >
> > The function machine_get_loadparm() is supposed to produce a C-string,
> > that is a NUL-terminated one, but it does not. ElectricFence can detect
> > this problem if the loadparm machine property is used.
> >
> > Let us make the returned string a NUL-terminated one.
> >
> > Fixes: 7104bae9de ("hw/s390x: provide loadparm property for the machine")
> > Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> > Reviewed-by: Thomas Huth <thuth@redhat.com>
> > Message-Id: <20200723162717.88485-1-pasic@linux.ibm.com>
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> >  hw/s390x/s390-virtio-ccw.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> > index 8cc2f25d8a6a..403d30e13bca 100644
> > --- a/hw/s390x/s390-virtio-ccw.c
> > +++ b/hw/s390x/s390-virtio-ccw.c
> > @@ -701,8 +701,12 @@ bool hpage_1m_allowed(void)
> >  static char *machine_get_loadparm(Object *obj, Error **errp)
> >  {
> >      S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
> > +    char *loadparm_str;
> >
> > -    return g_memdup(ms->loadparm, sizeof(ms->loadparm));
> > +    /* make a NUL-terminated string */
> > +    loadparm_str = g_memdup(ms->loadparm, sizeof(ms->loadparm) + 1);
> > +    loadparm_str[sizeof(ms->loadparm)] = 0;
> > +    return loadparm_str;  
> 
> Hi. Coverity points out (CID 1431058) that this code now
> reads off the end of the ms->loadparm buffer, because
> g_memdup() is going to read and copy 9 bytes (size + 1)
> and the array itself is only 8 bytes.
> 
> I don't think you can use g_memdup() here -- you need to
> allocate the memory with g_malloc() and then fill it with
> memcpy(), something like:
> 
>     loadparm_str = g_malloc(sizeof(ms->loadparm) + 1);
>     memcpy(loadparm_str, ms->loadparm, sizeof(ms->loadparm));
>     loadparm_str[sizeof(ms->loadparm)] = 0;

Sigh.

Halil, do you have time to cook up a patch?