Re: [PATCH v1 1/1] baseband/acc: fix check after deref and dead code

[David Marchand <david.marchand@redhat.com>]

On Thu, Nov 3, 2022 at 8:57 PM Hernan Vargas <hernan.vargas@intel.com> wrote:
>
> Fix potential issue of dereferencing a pointer before null check.
> Remove null check for value that could never be null.
>
> Coverity issue: 381646, 381631
> Fixes: 989dec301a9 ("baseband/acc100: add ring companion address")
>
> Signed-off-by: Hernan Vargas <hernan.vargas@intel.com>
> ---
>  drivers/baseband/acc/rte_acc100_pmd.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/drivers/baseband/acc/rte_acc100_pmd.c b/drivers/baseband/acc/rte_acc100_pmd.c
> index 96daef87bc..30a718916d 100644
> --- a/drivers/baseband/acc/rte_acc100_pmd.c
> +++ b/drivers/baseband/acc/rte_acc100_pmd.c
> @@ -4122,15 +4122,11 @@ acc100_dequeue_ldpc_enc(struct rte_bbdev_queue_data *q_data,
>         struct rte_bbdev_enc_op *op;
>         union acc_dma_desc *desc;
>
> -       if (q == NULL)
> -               return 0;

I guess this protects badly written applications that would do stuff
like pass an incorrect queue id, or call this callback while the queue
has not been configured yet.
This is something that should be caught at the bbdev layer (arguably
under the RTE_LIBRTE_BBDEV_DEBUG if the performance is that much
affected, though I'd like to see numbers).
(edit: I see Maxime replied a similar comment).

Back to this particular patch, rather than remove the check, the right
fix is to move acc_ring_avail_deq(q).
This is what Coverity reports.

And this same pattern is used in other parts of the driver.
It just happens that Coverity did not report them because some avec
under RTE_LIBRTE_BBDEV_DEBUG...



>  #ifdef RTE_LIBRTE_BBDEV_DEBUG
>         if (unlikely(ops == 0))

And I also noticed this hunk.

DPDK coding style, ops should be compared against NULL, but see below...


>                 return 0;
>  #endif
>         desc = q->ring_addr + (q->sw_ring_tail & q->sw_ring_wrap_mask);
> -       if (unlikely(desc == NULL))
> -               return 0;
>         op = desc->req.op_addr;
>         if (unlikely(ops == NULL || op == NULL))
>                 return 0;

... like here, so above check is redundant.

There is probably more cleanups to do in this driver.
This can be done later.


-- 
David Marchand