> On 13 Sep 2016, at 13:48 PM, P J P <ppan...@redhat.com> wrote: > > Hello Dmitry, > > +-- On Tue, 13 Sep 2016, Dmitry Fleytman wrote --+ > | > On 13 Sep 2016, at 10:00 AM, P J P <ppan...@redhat.com> wrote: > | > > | > +-- On Wed, 7 Sep 2016, P J P wrote --+ > | > | From: Prasad J Pandit <p...@fedoraproject.org> > | > | > | > | Vmware Paravirtual SCSI emulator while processing IO requests > | > | could run into an infinite loop if 'pvscsi_ring_pop_req_descr' > | > | always returned positive value. Limit IO loop to the maximum > | > | Do you see any specific scenario why this might happen? > > A guest user could set the 'ready_ptr' and 'PVSCSIRingInfo *mgr' parameter > in 'pvscsi_ring_pop_req_descr', such that it always returns true.
I see. The problematic code is if (ready_ptr != mgr->consumed_ptr) {…} mgr->consumed_ptr is managed by device and not visible to the driver, but ready_ptr is managed by driver and may be set to some “big” number. In this case it may take a lot of iterations for consumed_ptr to become equal to ready_ptr and additionally some requests will be send multiple times. The most straightforward way to fix this issue will be to check that ready_ptr - consumed_ptr is less than ring size. > > | > | Reported-by: Li Qiang <liqiang...@360.cn> > | > | pvscsi_process_io(PVSCSIState *s) > | > | { > | > | + int descr_pa_cnt = 0; > | > | PVSCSIRingReqDesc descr; > | > | hwaddr next_descr_pa; > | > | > | > | assert(s->rings_info_valid); > | > | - while ((next_descr_pa = pvscsi_ring_pop_req_descr(&s->rings)) != > 0) { > | > | + while (((next_descr_pa = pvscsi_ring_pop_req_descr(&s->rings)) != > 0) > | > | + && descr_pa_cnt++ < PVSCSI_SETUP_RINGS_MAX_NUM_PAGES) { > | > | Why do you limit number of processed descriptors by maximal number of pages > | in data exchange ring? What will happen to requests still waiting in the > | ring after this function exits? > > I limit it to maximum page count thinking that the descriptor value returned > by pvscsi_ring_pop_req_descr() is derived from the mgr->req_ring_pages_pa[] > array, which is of size 'PVSCSI_SETUP_RINGS_MAX_NUM_PAGES'. If > pvscsi_process_io() was to go into an infinite loop, it'd continue processing > the same set of req_ring_pages? I think you’re mixing concepts of number of pages in the ring and number of requests in the ring. Each page contains (much) more than one request. > > -- > Prasad J Pandit / Red Hat Product Security Team > 47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F