[PATCH] usb: core: config: Use struct_size() in kzalloc()

[Gustavo A. R. Silva]

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 = kzalloc(size, GFP_KERNEL);

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

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

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

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
---
 drivers/usb/core/config.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 7bb6b1bd06c8..20ff036b4c22 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -552,7 +552,7 @@ static int usb_parse_configuration(struct usb_device *dev, 
int cfgidx,
        unsigned char *buffer2;
        int size2;
        struct usb_descriptor_header *header;
-       int len, retval;
+       int retval;
        u8 inums[USB_MAXINTERFACES], nalts[USB_MAXINTERFACES];
        unsigned iad_num = 0;
 
@@ -707,8 +707,8 @@ static int usb_parse_configuration(struct usb_device *dev, 
int cfgidx,
                        nalts[i] = j = USB_MAXALTSETTING;
                }
 
-               len = sizeof(*intfc) + sizeof(struct usb_host_interface) * j;
-               config->intf_cache[i] = intfc = kzalloc(len, GFP_KERNEL);
+               intfc = kzalloc(struct_size(intfc, altsetting, j), GFP_KERNEL);
+               config->intf_cache[i] = intfc;
                if (!intfc)
                        return -ENOMEM;
                kref_init(&intfc->ref);
-- 
2.20.1