[PATCH] IB/cm: Use struct_size() in kmalloc()

[PATCH] IB/cm: Use struct_size() in kmalloc()

[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;
    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 <gustavo@embeddedor.com>
---
 drivers/infiniband/core/cm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index edb2cb758be7..af7f74faa448 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -4052,8 +4052,7 @@ static void cm_recv_handler(struct ib_mad_agent *mad_agent,
 	atomic_long_inc(&port->counter_group[CM_RECV].
 			counter[attr_id - CM_ATTR_ID_OFFSET]);
 
-	work = kmalloc(sizeof(*work) + sizeof(struct sa_path_rec) * paths,
-		       GFP_KERNEL);
+	work = kmalloc(struct_size(work, path, paths), GFP_KERNEL);
 	if (!work) {
 		ib_free_recv_mad(mad_recv_wc);
 		return;
-- 
2.20.1

Re: [PATCH] IB/cm: Use struct_size() in kmalloc()

[Jason Gunthorpe]

On Mon, Jan 07, 2019 at 11:26:16AM -0600, 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 <gustavo@embeddedor.com>
> ---
>  drivers/infiniband/core/cm.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Applied to for-next thanks

Jason