linux-kernel - Re: [bug] NULL pointer deref after 3f6634d997db ("iommu: Use right way to retrieve iommu

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Date:   Wed, 4 May 2022 09:11:08 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Jan Stancek <jstancek@...hat.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>, bgoncalv@...hat.com
Subject: Re: [bug] NULL pointer deref after 3f6634d997db ("iommu: Use right
 way to retrieve iommu_ops")

On Wed, May 04, 2022 at 12:14:07PM +0100, Robin Murphy wrote:
> On 2022-05-04 08:53, Jan Stancek wrote:
> [...]
> > Hi,
> > 
> > I'm getting panics after hunk above was applied in this patch
> > on ppc64le KVM guest, dev->iommu is NULL.
> 
> Oof, this can probably be hit with vfio-noiommu too, and by the look of
> things, `echo auto > /sys/kernel/iommu_groups/0/type` would likely blow
> up as well. Does the patch below work for you?
> 
> Thanks,
> Robin.
> 
> ----->8-----
> From abf0a38563bb2922a849e235d33d342170b5bc90 Mon Sep 17 00:00:00 2001
> Message-Id: <abf0a38563bb2922a849e235d33d342170b5bc90.1651662442.git.robin.murphy@....com>
> From: Robin Murphy <robin.murphy@....com>
> Date: Wed, 4 May 2022 11:53:20 +0100
> Subject: [PATCH] iommu: Make sysfs robust for non-API groups
> 
> Groups created by VFIO backends outside the core IOMMU API should never
> be passed directly into the API itself, however they still expose their
> standard sysfs attributes, so we can still stumble across them that way.
> Take care to consider those cases before jumping into our normal
> assumptions of a fully-initialised core API group.
> 
> Fixes: 3f6634d997db ("iommu: Use right way to retrieve iommu_ops")
> Reported-by: Jan Stancek <jstancek@...hat.com>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/iommu/iommu.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason