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

Dan Carpenter
2020-09-18T06:18:09Z

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@oracle.com> 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