2019-01-08 15:24:59

by Gustavo A. R. Silva

Subject: [PATCH] USB: core: urb: Use struct_size() in kmalloc()

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;
void *entry[];
};

instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

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

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

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
drivers/usb/core/urb.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index f51750bcd152..0eab79f82ce4 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -70,9 +70,8 @@ struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
{
struct urb *urb;

- urb = kmalloc(sizeof(struct urb) +
- iso_packets * sizeof(struct usb_iso_packet_descriptor),
- mem_flags);
+ urb = kmalloc(struct_size(urb, iso_frame_desc, iso_packets),
+ mem_flags);
if (!urb)
return NULL;
usb_init_urb(urb);
--
2.20.1

2019-01-08 17:39:30

by Alan Stern

Subject: Re: [PATCH] USB: core: urb: Use struct_size() in kmalloc()

On Tue, 8 Jan 2019, Gustavo A. R. Silva wrote:

> 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;
> void *entry[];
> };
>
> instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
>
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
>
> instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
>
> This code was detected with the help of Coccinelle.
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> drivers/usb/core/urb.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
> index f51750bcd152..0eab79f82ce4 100644
> --- a/drivers/usb/core/urb.c
> +++ b/drivers/usb/core/urb.c
> @@ -70,9 +70,8 @@ struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
> {
> struct urb *urb;
>
> - urb = kmalloc(sizeof(struct urb) +
> - iso_packets * sizeof(struct usb_iso_packet_descriptor),
> - mem_flags);
> + urb = kmalloc(struct_size(urb, iso_frame_desc, iso_packets),
> + mem_flags);
> if (!urb)
> return NULL;
> usb_init_urb(urb);

Acked-by: Alan Stern <[email protected]>