On Tue, 22 Aug 2017 15:39:04 +0200
Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> On 22/08/2017 03:07, nixiaoming wrote:
> > The error parameter passed through the external interface
> > causes the system oops. So it is necessary to increase the
> > parameter check for all EXPORT_SYMBOL_GPL
> >
> > example:
> > int irq_bypass_register_producer(struct irq_bypass_producer *producer)
> > {
> > if (!producer->token) /* oops if producer == null */
> > return -einval;
> > }
> > EXPORT_SYMBOL_GPL(irq_bypass_register_producer);
>
> This is used like this:
>
> drivers/vfio/pci/vfio_pci_intrs.c: irq_bypass_unregister_producer(&vdev->ctx[vector].producer);
> drivers/vfio/pci/vfio_pci_intrs.c: ret = irq_bypass_register_producer(&vdev->ctx[vector].producer);
> virt/kvm/eventfd.c: irq_bypass_unregister_consumer(&irqfd->consumer);
> virt/kvm/eventfd.c: ret = irq_bypass_register_consumer(&irqfd->consumer);
>
> So your check won't actually catch irqfd or vdev being NULL.
Additionally, I don't know of a reference to how extensively we should
harden these sorts of interfaces to misuse. Just because a symbol is
exported doesn't necessarily mean that the function needs to be
hardened against misuse as we might for an interface exposed to a
user. It's called by kernel mode code which can already do anything
it pleases to cause an oops. If such hardening makes the calling
conventions or code flow easier, or results in a function that's easier
to use correctly or harder to misuse, then I think it's justified. None
of that has been proven here and certainly doesn't seem to be the case
based on the current in-tree users. Can the patch submitter justify
that this is "necessary" as claimed in the commit log? Thanks,
Alex
> > Signed-off-by: nixiaoming <nixiaoming@xxxxxxxxxx>
> > ---
> > virt/lib/irqbypass.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/virt/lib/irqbypass.c b/virt/lib/irqbypass.c
> > index 6d2fcd6..2bb99e8 100644
> > --- a/virt/lib/irqbypass.c
> > +++ b/virt/lib/irqbypass.c
> > @@ -89,7 +89,7 @@ int irq_bypass_register_producer(struct irq_bypass_producer *producer)
> > struct irq_bypass_producer *tmp;
> > struct irq_bypass_consumer *consumer;
> >
> > - if (!producer->token)
> > + if (!producer || !producer->token)
> > return -EINVAL;
> >
> > might_sleep();
> > @@ -139,7 +139,7 @@ void irq_bypass_unregister_producer(struct irq_bypass_producer *producer)
> > struct irq_bypass_producer *tmp;
> > struct irq_bypass_consumer *consumer;
> >
> > - if (!producer->token)
> > + if (!producer || !producer->token)
> > return;
> >
> > might_sleep();
> > @@ -183,7 +183,7 @@ int irq_bypass_register_consumer(struct irq_bypass_consumer *consumer)
> > struct irq_bypass_consumer *tmp;
> > struct irq_bypass_producer *producer;
> >
> > - if (!consumer->token ||
> > + if (!consumer || !consumer->token ||
> > !consumer->add_producer || !consumer->del_producer)
> > return -EINVAL;
> >
> > @@ -234,7 +234,7 @@ void irq_bypass_unregister_consumer(struct irq_bypass_consumer *consumer)
> > struct irq_bypass_consumer *tmp;
> > struct irq_bypass_producer *producer;
> >
> > - if (!consumer->token)
> > + if (!consumer || !consumer->token)
> > return;
> >
> > might_sleep();
> >
>
