Re: [bug] NULL pointer deref after 3f6634d997db ("iommu: Use right way to retrieve iommu_ops")

[Jason Gunthorpe]

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@xxxxxxx>
> From: Robin Murphy <robin.murphy@xxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> ---
>  drivers/iommu/iommu.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason