[PATCH 4.9 076/101] xen/xenbus: fix return type in xenbus_file_read()

[Greg Kroah-Hartman]

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit 32ad11127b95236dfc52375f3707853194a7f4b4 upstream.

This code tries to store -EFAULT in an unsigned int.  The
xenbus_file_read() function returns type ssize_t so the negative value
is returned as a positive value to the user.

This change forces another change to the min() macro.  Originally, the
min() macro used "unsigned" type which checkpatch complains about.  Also
unsigned type would break if "len" were not capped at MAX_RW_COUNT.  Use
size_t for the min().  (No effect on runtime for the min_t() change).

Fixes: 2fb3683e7b16 ("xen: Add xenbus device driver")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Link: https://lore.kernel.org/r/YutxJUaUYRG/VLVc@kili
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/xen/xenbus/xenbus_dev_frontend.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -122,7 +122,7 @@ static ssize_t xenbus_file_read(struct f
 {
 	struct xenbus_file_priv *u = filp->private_data;
 	struct read_buffer *rb;
-	unsigned i;
+	ssize_t i;
 	int ret;
 
 	mutex_lock(&u->reply_mutex);
@@ -142,7 +142,7 @@ again:
 	rb = list_entry(u->read_buffers.next, struct read_buffer, list);
 	i = 0;
 	while (i < len) {
-		unsigned sz = min((unsigned)len - i, rb->len - rb->cons);
+		size_t sz = min_t(size_t, len - i, rb->len - rb->cons);
 
 		ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz);