[PATCH 5.4 095/111] rapidio: fix an error in get_user_pages_fast() error handling

[Greg Kroah-Hartman]

From: John Hubbard <jhubbard@xxxxxxxxxx>

commit ffca476a0a8d26de767cc41d62b8ca7f540ecfdd upstream.

In the case of get_user_pages_fast() returning fewer pages than
requested, rio_dma_transfer() does not quite do the right thing.  It
attempts to release all the pages that were requested, rather than just
the pages that were pinned.

Fix the error handling so that only the pages that were successfully
pinned are released.

Fixes: e8de370188d0 ("rapidio: add mport char device driver")
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Matt Porter <mporter@xxxxxxxxxxxxxxxxxxx>
Cc: Alexandre Bounine <alex.bou9@xxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20200517235620.205225-2-jhubbard@xxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/rapidio/devices/rio_mport_cdev.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -877,6 +877,11 @@ rio_dma_transfer(struct file *filp, u32
 				rmcd_error("pinned %ld out of %ld pages",
 					   pinned, nr_pages);
 			ret = -EFAULT;
+			/*
+			 * Set nr_pages up to mean "how many pages to unpin, in
+			 * the error handler:
+			 */
+			nr_pages = pinned;
 			goto err_pg;
 		}