Re: [PATCH v0 39/42] crypto: ccree - check notifier registration return value

Cristian Marussi
2021-11-12T18:32:38Z

On Mon, Nov 08, 2021 at 11:11:54AM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
>
> Avoid homegrown notifier registration checks.
>
> No functional changes.
>

Hi Borislav,

> Signed-off-by: Borislav Petkov <bp@suse.de>
> Cc: linux-crypto@vger.kernel.org
> ---
> drivers/crypto/ccree/cc_fips.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/crypto/ccree/cc_fips.c b/drivers/crypto/ccree/cc_fips.c
> index 702aefc21447..de842da7d51c 100644
> --- a/drivers/crypto/ccree/cc_fips.c
> +++ b/drivers/crypto/ccree/cc_fips.c
> @@ -146,7 +146,9 @@ int cc_fips_init(struct cc_drvdata *p_drvdata)
> tasklet_init(&fips_h->tasklet, fips_dsr, (unsigned long)p_drvdata);
> fips_h->drvdata = p_drvdata;
> fips_h->nb.notifier_call = cc_ree_fips_failure;
> - atomic_notifier_chain_register(&fips_fail_notif_chain, &fips_h->nb);
> +
> + if (atomic_notifier_chain_register(&fips_fail_notif_chain, &fips_h->nb))
> + pr_warn("Failure notifier already registered\n");
>

Looking at the implementation of atomic_notifier_chain_register() and
its internal helper down below, I can see that atomic_notifier_chain_register()
ALWAYS return 0 (O_o) and anyway there is a WARN() in the notifiier core already
to alert of double registrations.

What is the aim of this patch ?
It's not clear from the commit message what are you trying to achieve.
Am I missing something ?
(Is it to circumvent some static checker to avoid this false positive ?
just guessing...)

Thanks,
Cristian

-----8<----------
static int notifier_chain_register(struct notifier_block **nl,
struct notifier_block *n)
{
while ((*nl) != NULL) {
if (unlikely((*nl) == n)) {
WARN(1, "double register detected");
return 0;
}
if (n->priority > (*nl)->priority)
break;
nl = &((*nl)->next);
}
n->next = *nl;
rcu_assign_pointer(*nl, n);
return 0;
}

/**
* atomic_notifier_chain_register - Add notifier to an atomic notifier chain
* @nh: Pointer to head of the atomic notifier chain
* @n: New entry in notifier chain
*
* Adds a notifier to an atomic notifier chain.
*
* Currently always returns zero.
*/
int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
struct notifier_block *n)
{
unsigned long flags;
int ret;

spin_lock_irqsave(&nh->lock, flags);
ret = notifier_chain_register(&nh->head, n);
spin_unlock_irqrestore(&nh->lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(atomic_notifier_chain_register);
------