[PATCH][next] usb: gadget: f_phonet: Use struct_size() helper in kzalloc()

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Make use of the struct_size() helper instead of an open-coded version,
in order to avoid any potential type mistakes or integer overflows that,
in the worst scenario, could lead to heap overflows.

Also, address the following sparse warnings:
drivers/usb/gadget/function/f_phonet.c:673:16: warning: using sizeof on a flexible structure

Link: https://github.com/KSPP/linux/issues/160
Link: https://github.com/KSPP/linux/issues/174
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/usb/gadget/function/f_phonet.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/function/f_phonet.c b/drivers/usb/gadget/function/f_phonet.c
index 068ed8417e5a..0bebbdf3f213 100644
--- a/drivers/usb/gadget/function/f_phonet.c
+++ b/drivers/usb/gadget/function/f_phonet.c
@@ -668,10 +668,8 @@ static struct usb_function *phonet_alloc(struct usb_function_instance *fi)
 {
 	struct f_phonet *fp;
 	struct f_phonet_opts *opts;
-	int size;
 
-	size = sizeof(*fp) + (phonet_rxq_size * sizeof(struct usb_request *));
-	fp = kzalloc(size, GFP_KERNEL);
+	fp = kzalloc(struct_size(fp, out_reqv, phonet_rxq_size), GFP_KERNEL);
 	if (!fp)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.27.0