On 21/01/2020 09:10, Tyrel Datwyler wrote:
> From: Tyrel Datwyler
>
> Commit e5afdf9dd515 ("powerpc/vfio_spapr_tce: Add reference counting to
> iommu_table") missed an iommu_table allocation in the pseries vio code.
> The iommu_table is allocated with kzalloc and as a result the associated
> kref gets a value of zero. This has the side effect that during a DLPAR
> remove of the associated virtual IOA the iommu_tce_table_put() triggers
> a use-after-free underflow warning.
>
> Call Trace:
> [c002879e39f0] [c071ecb4] refcount_warn_saturate+0x184/0x190
> (unreliable)
> [c002879e3a50] [c00500ac] iommu_tce_table_put+0x9c/0xb0
> [c002879e3a70] [c00f54e4] vio_dev_release+0x34/0x70
> [c002879e3aa0] [c087cfa4] device_release+0x54/0xf0
> [c002879e3b10] [c0d64c84] kobject_cleanup+0xa4/0x240
> [c002879e3b90] [c087d358] put_device+0x28/0x40
> [c002879e3bb0] [c07a328c] dlpar_remove_slot+0x15c/0x250
> [c002879e3c50] [c07a348c] remove_slot_store+0xac/0xf0
> [c002879e3cd0] [c0d64220] kobj_attr_store+0x30/0x60
> [c002879e3cf0] [c04ff13c] sysfs_kf_write+0x6c/0xa0
> [c002879e3d10] [c04fde4c] kernfs_fop_write+0x18c/0x260
> [c002879e3d60] [c0410f3c] __vfs_write+0x3c/0x70
> [c002879e3d80] [c0415408] vfs_write+0xc8/0x250
> [c002879e3dd0] [c04157dc] ksys_write+0x7c/0x120
> [c002879e3e20] [c000b278] system_call+0x5c/0x68
>
> Further, since the refcount was always zero the iommu_tce_table_put()
> fails to call the iommu_table release function resulting in a leak.
>
> Fix this issue be initilizing the iommu_table kref immediately after
> allocation.
>
> Fixes: e5afdf9dd515 ("powerpc/vfio_spapr_tce: Add reference counting to
> iommu_table")
> Signed-off-by: Tyrel Datwyler
Reviewed-by: Alexey Kardashevskiy
> ---
> arch/powerpc/platforms/pseries/vio.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/vio.c
> b/arch/powerpc/platforms/pseries/vio.c
> index 79e2287..f682b7b 100644
> --- a/arch/powerpc/platforms/pseries/vio.c
> +++ b/arch/powerpc/platforms/pseries/vio.c
> @@ -1176,6 +1176,8 @@ static struct iommu_table *vio_build_iommu_table(struct
> vio_dev *dev)
> if (tbl == NULL)
> return NULL;
>
> + kref_init(>it_kref);
> +
> of_parse_dma_window(dev->dev.of_node, dma_window,
> >it_index, , );
>
>
--
Alexey