Re: [PATCH v2 4/5] libvhost-user: prevent over-running max RAM slots

[Raphael Norwitz <raphael.norwitz@nutanix.com>]

On Mon, Jan 10, 2022 at 04:40:08AM -0500, Michael S. Tsirkin wrote:
> On Thu, Jan 06, 2022 at 06:47:35AM +0000, Raphael Norwitz wrote:
> > When VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS support was added to
> > libvhost-user, no guardrails were added to protect against QEMU
> > attempting to hot-add too many RAM slots to a VM with a libvhost-user
> > based backed attached.
> > 
> > This change adds the missing error handling by introducing a check on
> > the number of RAM slots the device has available before proceeding to
> > process the VHOST_USER_ADD_MEM_REG message.
> > 
> > Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> > ---
> >  subprojects/libvhost-user/libvhost-user.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/subprojects/libvhost-user/libvhost-user.c b/subprojects/libvhost-user/libvhost-user.c
> > index 77ddc96ddf..0fe3aa155b 100644
> > --- a/subprojects/libvhost-user/libvhost-user.c
> > +++ b/subprojects/libvhost-user/libvhost-user.c
> > @@ -690,6 +690,11 @@ vu_add_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
> >      VuDevRegion *dev_region = &dev->regions[dev->nregions];
> >      void *mmap_addr;
> >  
> > +    if (dev->nregions == VHOST_USER_MAX_RAM_SLOTS) {
> > +        vu_panic(dev, "No free ram slots available");
> 
> A bit more verbose maybe? Describe what happened to trigger this?
> e.g. adding a region with no free ram slots?
>

Ack

> > +        return false;
> > +    }
> > +
> >      if (vmsg->fd_num != 1 ||
> >          vmsg->size != sizeof(vmsg->payload.memreg)) {
> >          vu_panic(dev, "VHOST_USER_REM_MEM_REG received multiple regions");
> > -- 
> > 2.20.1
>