-----Original Message-----
From: Michael Kelley (LINUX) <redacted>
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
[off-list ref]; KY Srinivasan [off-list ref]; Paul Rosswurm
[off-list ref]; 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 <redacted> On Behalf Of Haiyang Zhang
Sent: Thursday, January 26, 2023 1:05 PM

quoted

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