Re: [PATCH RESEND] scsi: libfc: Use refcount_* APIs for reference count management

[Deepak R Varma]

On Wed, Mar 01, 2023 at 02:28:49PM -0500, James Bottomley wrote:
> On Thu, 2023-03-02 at 00:32 +0530, Deepak R Varma wrote:
> > The atomic_t API based object reference counter management is prone
> > to counter value overflows, object use-after-free issues and to
> > return puzzling values. The improved refcount_t APIs are designed to
> > address these known issues with atomic_t reference counter
> > management. This white paper [1] has detailed reasons for moving from
> > atomic_t to refcount_t APIs. Hence replace the atomic_* based
> > implementation by its refcount_* based equivalent.
> > The issue is identified using atomic_as_refcounter.cocci Coccinelle
> > semantic patch script.
> > 
> >         [1] https://arxiv.org/pdf/1710.06175.pdf
> 
> Citing long whitepapers in support of a patch isn't helpful to time
> pressed reviewers, particularly when it's evident you didn't understand
> the paper you cite. The argument in the paper for replacing atomics
> with refcounts can be summarized as: if a user can cause a counter
> overflow in an atomic_t simply by performing some action from userspace
> then that represents a source of potential overflow attacks on the
> kernel which should be mitigated by replacing the atomic_t in question
> with a refcount_t which is overflow resistant.
> 
> What's missing from the quoted changelog is a justification of how a
> user could cause an overflow in the ex_refcnt atomic_t.

Thank you very much James for the review comments. I truly appreciate your time
and guidance. I will study your feedback and send in a revision with necessary
update to patch log.

Regards,
./drv

> 
> James
>