misc: mic: scif: Fix error handling path

Inside __scif_pin_pages(), when map_flags != SCIF_MAP_KERNEL it
will call pin_user_pages_fast() to map nr_pages. However,
pin_user_pages_fast() might fail with a return value -ERRNO.

The return value is stored in pinned_pages->nr_pages. which in
turn is passed to unpin_user_pages(), which expects
pinned_pages->nr_pages >=0, else disaster.

Fix this by assigning pinned_pages->nr_pages to 0 if
pin_user_pages_fast() returns -ERRNO.

Fixes: ba612aa8 ("misc: mic: SCIF memory registration and unregistration")
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Signed-off-by: NSouptick Joarder <jrdr.linux@gmail.com>
Link: https://lore.kernel.org/r/1600570295-29546-1-git-send-email-jrdr.linux@gmail.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mic/scif/scif_rma.c

@@ -1392,6 +1392,8 @@ int __scif_pin_pages(void *addr, size_t len, int *out_prot,
 				(prot & SCIF_PROT_WRITE) ? FOLL_WRITE : 0,
 				pinned_pages->pages);
 		if (nr_pages != pinned_pages->nr_pages) {
+			if (pinned_pages->nr_pages < 0)
+				pinned_pages->nr_pages = 0;
 			if (try_upgrade) {
 				if (ulimit)
 					__scif_dec_pinned_vm_lock(mm, nr_pages);
@@ -1408,7 +1410,6 @@ int __scif_pin_pages(void *addr, size_t len, int *out_prot,
 
 	if (pinned_pages->nr_pages < nr_pages) {
 		err = -EFAULT;
-		pinned_pages->nr_pages = nr_pages;
 		goto dec_pinned;
 	}
 
@@ -1421,7 +1422,6 @@ int __scif_pin_pages(void *addr, size_t len, int *out_prot,
 		__scif_dec_pinned_vm_lock(mm, nr_pages);
 	/* Something went wrong! Rollback */
 error_unmap:
-	pinned_pages->nr_pages = nr_pages;
 	scif_destroy_pinned_pages(pinned_pages);
 	*pages = NULL;
 	dev_dbg(scif_info.mdev.this_device,