RE: [PATCH net, 2/2] net: mana: Fix accessing freed irq affinity_hint

[Haiyang Zhang <haiyangz@microsoft.com>]

> -----Original Message-----
> From: Haiyang Zhang <haiyangz@microsoft.com>
> Sent: Sunday, January 29, 2023 1:51 PM
> To: Michael Kelley (LINUX) <mikelley@microsoft.com>; linux-
> hyperv@vger.kernel.org; netdev@vger.kernel.org
> Cc: Dexuan Cui <decui@microsoft.com>; KY Srinivasan <kys@microsoft.com>;
> Paul Rosswurm <paulros@microsoft.com>; olaf@aepfle.de;
> vkuznets@redhat.com; davem@davemloft.net; linux-kernel@vger.kernel.org;
> stable@vger.kernel.org
> Subject: RE: [PATCH net, 2/2] net: mana: Fix accessing freed irq affinity_hint
> 
> 
> 
> > -----Original Message-----
> > From: Michael Kelley (LINUX) <mikelley@microsoft.com>
> > Sent: Sunday, January 29, 2023 9:27 AM
> > To: Haiyang Zhang <haiyangz@microsoft.com>; linux-
> hyperv@vger.kernel.org;
> > netdev@vger.kernel.org
> > Cc: Haiyang Zhang <haiyangz@microsoft.com>; Dexuan Cui
> > <decui@microsoft.com>; KY Srinivasan <kys@microsoft.com>; Paul
> Rosswurm
> > <paulros@microsoft.com>; olaf@aepfle.de; vkuznets@redhat.com;
> > davem@davemloft.net; linux-kernel@vger.kernel.org;
> stable@vger.kernel.org
> > Subject: RE: [PATCH net, 2/2] net: mana: Fix accessing freed irq affinity_hint
> >
> > From: LKML haiyangz <lkmlhyz@microsoft.com> On Behalf Of Haiyang
> Zhang
> > Sent: Thursday, January 26, 2023 1:05 PM
> > >
> > > After calling irq_set_affinity_and_hint(), the cpumask pointer is
> > > saved in desc->affinity_hint, and will be used later when reading
> > > /proc/irq/<num>/affinity_hint. So the cpumask variable needs to be
> > > allocated per irq, and available until freeing the irq. Otherwise,
> > > we are accessing freed memory when reading the affinity_hint file.
> > >
> > > To fix the bug, allocate the cpumask per irq, and free it just
> > > before freeing the irq.
> >
> > Since the cpumask being passed to irq_set_affinity_and_hint()
> > always contains exactly one CPU, the code can be considerably
> > simplified by using the pre-calculated and persistent masks
> > available as cpumask_of(cpu).  All allocation of cpumasks in this
> > code goes away, and you can set the affinity_hint to NULL in the
> > cleanup and remove paths without having to free any masks.
> >
> Great idea!
> Will update the patch accordingly.

Also, I saw this alloc isn't necessary either:
	cpus = kcalloc(nvec, sizeof(*cpus), GFP_KERNEL);

We can simply use the return from cpumask_local_spread()
without saving all cpu numbers in a tmp array.

I will clean this up too :)

Thanks,
- Haiyang