[PATCH] usbip: usbip_host_common: Use struct_size() in realloc()

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Valentina Manea <valentina.manea.m@gmail.com>,
	Shuah Khan <shuah@kernel.org>
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH] usbip: usbip_host_common: Use struct_size() in realloc()
Date: Thu, 23 May 2019 09:40:19 -0500	[thread overview]
Message-ID: <20190523144019.GA28932@embeddedor> (raw)

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
    int stuff;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = realloc(instance, size);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

size = struct_size(instance, entry, count);

or

instance = realloc(instance, struct_size(instance, entry, count));

Notice that, in this case, variable size is not necessary,
hence it is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---

Notice that checkpatch reports the following warning:

WARNING: line over 80 characters
#57: FILE: tools/usb/usbip/libsrc/usbip_host_common.c:90:
+	edev = realloc(edev, struct_size(edev, uinf, edev->udev.bNumInterfaces));

The line above is 81-character long. So, I think we should be fine
with that, instead of split it into two lines like:

edev = realloc(edev,
	       struct_size(edev, uinf, edev->udev.bNumInterfaces));

Thanks
--
Gustavo

 tools/usb/usbip/libsrc/usbip_host_common.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/tools/usb/usbip/libsrc/usbip_host_common.c b/tools/usb/usbip/libsrc/usbip_host_common.c
index 2813aa821c82..1645d02a52af 100644
--- a/tools/usb/usbip/libsrc/usbip_host_common.c
+++ b/tools/usb/usbip/libsrc/usbip_host_common.c
@@ -67,7 +67,6 @@ struct usbip_exported_device *usbip_exported_device_new(
 {
 	struct usbip_exported_device *edev = NULL;
 	struct usbip_exported_device *edev_old;
-	size_t size;
 	int i;
 
 	edev = calloc(1, sizeof(struct usbip_exported_device));
@@ -87,11 +86,8 @@ struct usbip_exported_device *usbip_exported_device_new(
 		goto err;
 
 	/* reallocate buffer to include usb interface data */
-	size = sizeof(struct usbip_exported_device) +
-		edev->udev.bNumInterfaces * sizeof(struct usbip_usb_interface);
-
 	edev_old = edev;
-	edev = realloc(edev, size);
+	edev = realloc(edev, struct_size(edev, uinf, edev->udev.bNumInterfaces));
 	if (!edev) {
 		edev = edev_old;
 		dbg("realloc failed");
-- 
2.21.0

