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Date:   Thu, 17 Sep 2020 15:39:51 +0300
From:   Dan Carpenter <dan.carpenter@oracle.com>
To:     Souptick Joarder <jrdr.linux@gmail.com>, jhubbard@nvidia.com
Cc:     mporter@kernel.crashing.org, alex.bou9@gmail.com,
        akpm@linux-foundation.org, gustavoars@kernel.org,
        madhuparnabhowmik10@gmail.com, linux-kernel@vger.kernel.org,
        Ira Weiny <ira.weiny@intel.com>,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [linux-next PATCH] rapidio: Fix error handling path
Message-ID: <20200917123951.GP18329@kadam>
References: <1600227737-20785-1-git-send-email-jrdr.linux@gmail.com>
 <20200916100232.GF18329@kadam>
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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