Re: [linux-next PATCH] rapidio: Fix error handling path

[Dan Carpenter]

On Fri, Sep 18, 2020 at 07:55:05AM +0530, Souptick Joarder wrote:
> Hi Dan,
> 
> On Thu, Sep 17, 2020 at 6:10 PM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> >
> > On Wed, Sep 16, 2020 at 01:02:32PM +0300, Dan Carpenter wrote:
> > > On Wed, Sep 16, 2020 at 09:12:17AM +0530, Souptick Joarder wrote:
> > > > There is an error when pin_user_pages_fast() returns -ERRNO and
> > > > inside error handling path driver end up calling unpin_user_pages()
> > > > with -ERRNO which is not correct.
> > > >
> > > > This patch will fix the problem.
> > >
> > > There are a few ways we could prevent bug in the future.
> > >
> > > 1) This could have been caught with existing static analysis tools
> > >    which warn about when a value is set but not used.
> > >
> > > 2) I've created a Smatch check which warngs about:
> > >
> > >       drivers/rapidio/devices/rio_mport_cdev.c:955 rio_dma_transfer() warn: unpinning negative pages 'nr_pages'
> > >
> > >    I'll test it out tonight and see how well it works.  I don't
> > >    immediately see any other bugs allthough Smatch doesn't like the code
> > >    in siw_umem_release().  It uses "min_t(int" which suggests that
> > >    negative pages are okay.
> > >
> > >          int to_free = min_t(int, PAGES_PER_CHUNK, num_pages);
> > >
> >
> > I only found one bug but I'm going to add unpin_user_pages_dirty_lock()
> > to the mix a retest.  There were a few other false positives.  In
> > reviewing the code, I noticed that orangefs_bufmap_map() is also buggy.
> >
> > I sort of feel like returning partial successes is not working.  We
> > could easily make a wrapper which either pins everything or it returns
> > an error code.
> >
> > drivers/misc/mic/scif/scif_rma.c:1399 __scif_pin_pages() warn: unpinning negative pages 'pinned_pages->nr_pages'
> >
> > drivers/misc/mic/scif/scif_rma.c
> >   1355                          vmalloc_addr = true;
> >   1356
> >   1357                  for (i = 0; i < nr_pages; i++) {
> >   1358                          if (vmalloc_addr)
> >   1359                                  pinned_pages->pages[i] =
> >   1360                                          vmalloc_to_page(addr + (i * PAGE_SIZE));
> >   1361                          else
> >   1362                                  pinned_pages->pages[i] =
> >   1363                                          virt_to_page(addr + (i * PAGE_SIZE));
> >   1364                  }
> >   1365                  pinned_pages->nr_pages = nr_pages;
> >   1366                  pinned_pages->map_flags = SCIF_MAP_KERNEL;
> >   1367          } else {
> >   1368                  /*
> >   1369                   * SCIF supports registration caching. If a registration has
> >   1370                   * been requested with read only permissions, then we try
> >   1371                   * to pin the pages with RW permissions so that a subsequent
> >   1372                   * transfer with RW permission can hit the cache instead of
> >   1373                   * invalidating it. If the upgrade fails with RW then we
> >   1374                   * revert back to R permission and retry
> >   1375                   */
> >   1376                  if (prot == SCIF_PROT_READ)
> >   1377                          try_upgrade = true;
> >   1378                  prot |= SCIF_PROT_WRITE;
> >   1379  retry:
> >   1380                  mm = current->mm;
> >   1381                  if (ulimit) {
> >   1382                          err = __scif_check_inc_pinned_vm(mm, nr_pages);
> >   1383                          if (err) {
> >   1384                                  pinned_pages->nr_pages = 0;
> >   1385                                  goto error_unmap;
> >   1386                          }
> >   1387                  }
> >   1388
> >   1389                  pinned_pages->nr_pages = pin_user_pages_fast(
> >   1390                                  (u64)addr,
> >   1391                                  nr_pages,
> >   1392                                  (prot & SCIF_PROT_WRITE) ? FOLL_WRITE : 0,
> >   1393                                  pinned_pages->pages);
> >   1394                  if (nr_pages != pinned_pages->nr_pages) {
> >   1395                          if (try_upgrade) {
> >   1396                                  if (ulimit)
> >   1397                                          __scif_dec_pinned_vm_lock(mm, nr_pages);
> >   1398                                  /* Roll back any pinned pages */
> >   1399                                  unpin_user_pages(pinned_pages->pages,
> >   1400                                                   pinned_pages->nr_pages);
> >                                                          ^^^^^^^^^^^^^^^^^^^^^^
> > Negative.
> >
> >   1401                                  prot &= ~SCIF_PROT_WRITE;
> >   1402                                  try_upgrade = false;
> >   1403                                  goto retry;
> >   1404                          }
> >   1405                  }
> >   1406                  pinned_pages->map_flags = 0;
> >   1407          }
> >   1408
> >   1409          if (pinned_pages->nr_pages < nr_pages) {
> >                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > These are both signed so it negative ->nr_pages are less than nr_pages.
> >
> >   1410                  err = -EFAULT;
> >   1411                  pinned_pages->nr_pages = nr_pages;
> >                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > This sets it to "everything was pinned".
> >
> >   1412                  goto dec_pinned;
> >   1413          }
> >   1414
> >   1415          *out_prot = prot;
> >   1416          atomic_set(&pinned_pages->ref_count, 1);
> >   1417          *pages = pinned_pages;
> >   1418          return err;
> >   1419  dec_pinned:
> >   1420          if (ulimit)
> >   1421                  __scif_dec_pinned_vm_lock(mm, nr_pages);
> >   1422          /* Something went wrong! Rollback */
> >   1423  error_unmap:
> >   1424          pinned_pages->nr_pages = nr_pages;
> >                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > This assumes everything was pinned successfully.
> >
> >   1425          scif_destroy_pinned_pages(pinned_pages);
> >                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > We absolutely don't want to pass negative ->nr_pages to this function
> > either.
> >
> >   1426          *pages = NULL;
> >   1427          dev_dbg(scif_info.mdev.this_device,
> >   1428                  "%s %d err %d len 0x%lx\n", __func__, __LINE__, err, len);
> >   1429          return err;
> >   1430  }
> >
> > regards,
> > dan carpenter
> 
> 
> I have drafted a patch for this bug. Shall I post it ?

Absolutely, please.  :)

regards,
dan carpenter