From:   Haiyang Zhang <haiyangz@microsoft.com>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "netdev@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" <olaf@aepfle.de>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH net, 2/2] net: mana: Fix accessing freed irq affinity_hint
Thread-Topic: [PATCH net, 2/2] net: mana: Fix accessing freed irq
 affinity_hint
Thread-Index: AQHZMcn4aI2nsbHR902MpaNNd4HTWq61d9eAgABJsAA=
Date:   Sun, 29 Jan 2023 18:51:17 +0000
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> -----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
>=20
> 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.
>=20
> 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.
>=20
Great idea!
Will update the patch accordingly.

- Haiyang