[PATCH v2] drivers/fpga: use standard array-copy function

[Philipp Stanner <pstanner@redhat.com>]

dfl.c utilizes memdup_user() and array_size() to copy a userspace array.
array_size() will likely never trigger thanks to the preceeding check.
Nevertheless, in the theoretical event that it would, it would return
SIZE_MAX to memdup_user(), resulting in an attempt to allocate huge
amounts of memory.

string.h from the core-api now provides memdup_array_user() which also
performs an overflow check and returns an error-pointer with -EOVERFLOW
to the caller.
As an additional advantage it standardizes how userspace-arrays are
being copied and, thus, makes it more obvious to readers that an array
is being copied.

Replace memdup_user() with memdup_array_user().

Suggested-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
---
Changes in v2:
- Rewrite commit's name and message to clarify the patch's advantages
---
 drivers/fpga/dfl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c
index dd7a783d53b5..e69b9f1f2a50 100644
--- a/drivers/fpga/dfl.c
+++ b/drivers/fpga/dfl.c
@@ -2008,8 +2008,8 @@ long dfl_feature_ioctl_set_irq(struct platform_device *pdev,
 	    (hdr.start + hdr.count < hdr.start))
 		return -EINVAL;
 
-	fds = memdup_user((void __user *)(arg + sizeof(hdr)),
-			  array_size(hdr.count, sizeof(s32)));
+	fds = memdup_array_user((void __user *)(arg + sizeof(hdr)),
+				hdr.count, sizeof(s32));
 	if (IS_ERR(fds))
 		return PTR_ERR(fds);
 
-- 
2.41.0