md/raid10: prevent access of uninitialized resync_pages offset

commit 45422b704db392a6d79d07ee3e3670b11048bd53 upstream.

Due to unneeded multiplication in the out_free_pages portion of
r10buf_pool_alloc(), when using a 3-copy raid10 layout, it is
possible to access a resync_pages offset that has not been
initialized.  This access translates into a crash of the system
within resync_free_pages() while passing a bad pointer to
put_page().  Remove the multiplication, preventing access to the
uninitialized area.

Fixes: f0250618 ("md: raid10: don't use bio's vec table to manage resync pages")
Cc: stable@vger.kernel.org # 4.12+
Signed-off-by: NJohn Pittman <jpittman@redhat.com>
Suggested-by: NDavid Jeffery <djeffery@redhat.com>
Reviewed-by: NLaurence Oberman <loberman@redhat.com>
Signed-off-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/md/raid10.c

@@ -229,7 +229,7 @@ static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
 
 out_free_pages:
 	while (--j >= 0)
-		resync_free_pages(&rps[j * 2]);
+		resync_free_pages(&rps[j]);
 
 	j = 0;
 out_free_bio: