Re: [PATCH v3 2/3] RDMA/mana_ib: Prefer struct_size over open coded arithmetic

[Justin Stitt]

Hi,

On Sat, Apr 06, 2024 at 04:23:36PM +0200, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
> 
> As the "req" variable is a pointer to "struct mana_cfg_rx_steer_req_v2"
> and this structure ends in a flexible array:
> 
> struct mana_cfg_rx_steer_req_v2 {
> 	[...]
>         mana_handle_t indir_tab[] __counted_by(num_indir_entries);
> };
> 
> the preferred way in the kernel is to use the struct_size() helper to
> do the arithmetic instead of the calculation "size + size * count" in
> the kzalloc() function.
> 
> Moreover, use the "offsetof" helper to get the indirect table offset
> instead of the "sizeof" operator and avoid the open-coded arithmetic in
> pointers using the new flex member. This new structure member also allow
> us to remove the "req_indir_tab" variable since it is no longer needed.
> 
> This way, the code is more readable and safer.
> 
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/160 [2]
> Signed-off-by: Erick Archer <erick.archer@xxxxxxxxxxx>

Reviewed-by: Justin Stitt <justinstitt@xxxxxxxxxx>

> ---
>  drivers/infiniband/hw/mana/qp.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mana/qp.c b/drivers/infiniband/hw/mana/qp.c
> index ef0a6dc664d0..4cd8f8afe80d 100644
> --- a/drivers/infiniband/hw/mana/qp.c
> +++ b/drivers/infiniband/hw/mana/qp.c
> @@ -15,15 +15,13 @@ static int mana_ib_cfg_vport_steering(struct mana_ib_dev *dev,
>  	struct mana_port_context *mpc = netdev_priv(ndev);
>  	struct mana_cfg_rx_steer_req_v2 *req;
>  	struct mana_cfg_rx_steer_resp resp = {};
> -	mana_handle_t *req_indir_tab;
>  	struct gdma_context *gc;
>  	u32 req_buf_size;
>  	int i, err;
>  
>  	gc = mdev_to_gc(dev);
>  
> -	req_buf_size =
> -		sizeof(*req) + sizeof(mana_handle_t) * MANA_INDIRECT_TABLE_SIZE;
> +	req_buf_size = struct_size(req, indir_tab, MANA_INDIRECT_TABLE_SIZE);
>  	req = kzalloc(req_buf_size, GFP_KERNEL);
>  	if (!req)
>  		return -ENOMEM;
> @@ -44,20 +42,20 @@ static int mana_ib_cfg_vport_steering(struct mana_ib_dev *dev,
>  		req->rss_enable = true;
>  
>  	req->num_indir_entries = MANA_INDIRECT_TABLE_SIZE;
> -	req->indir_tab_offset = sizeof(*req);
> +	req->indir_tab_offset = offsetof(struct mana_cfg_rx_steer_req_v2,
> +					 indir_tab);
>  	req->update_indir_tab = true;
>  	req->cqe_coalescing_enable = 1;
>  
> -	req_indir_tab = (mana_handle_t *)(req + 1);
>  	/* The ind table passed to the hardware must have
>  	 * MANA_INDIRECT_TABLE_SIZE entries. Adjust the verb
>  	 * ind_table to MANA_INDIRECT_TABLE_SIZE if required
>  	 */
>  	ibdev_dbg(&dev->ib_dev, "ind table size %u\n", 1 << log_ind_tbl_size);
>  	for (i = 0; i < MANA_INDIRECT_TABLE_SIZE; i++) {
> -		req_indir_tab[i] = ind_table[i % (1 << log_ind_tbl_size)];
> +		req->indir_tab[i] = ind_table[i % (1 << log_ind_tbl_size)];
>  		ibdev_dbg(&dev->ib_dev, "index %u handle 0x%llx\n", i,
> -			  req_indir_tab[i]);
> +			  req->indir_tab[i]);
>  	}
>  
>  	req->update_hashkey = true;
> -- 
> 2.25.1
> 

Thanks
Justin