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

[Haiyang Zhang]

> -----Original Message-----
> From: Michael Kelley (LINUX) <mikelley@xxxxxxxxxxxxx>
> Sent: Sunday, January 29, 2023 9:27 AM
> To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; linux-hyperv@xxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx
> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; Dexuan Cui
> <decui@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Paul Rosswurm
> <paulros@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; vkuznets@xxxxxxxxxx;
> davem@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx
> Subject: RE: [PATCH net, 2/2] net: mana: Fix accessing freed irq affinity_hint
> 
> From: LKML haiyangz <lkmlhyz@xxxxxxxxxxxxx> 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.

- Haiyang