Re: [PATCH] powerpc/pseries/vio: Fix iommu_table use-after-free refcount warning

From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Tyrel Datwyler <tyreld@linux.ibm.com>, mpe@ellerman.id.au
Cc: drt@linux.ibm.com, linuxppc-dev@lists.ozlabs.org,
	Tyrel Datwyler <tyreld@linux.vnet.ibm.com>,
	david@gibson.dropbear.id.au
Subject: Re: [PATCH] powerpc/pseries/vio: Fix iommu_table use-after-free refcount warning
Date: Tue, 21 Jan 2020 14:45:18 +1100	[thread overview]
Message-ID: <1245e80e-3235-f88d-49bd-81244aad096a@ozlabs.ru> (raw)
In-Reply-To: <1579558202-26052-1-git-send-email-tyreld@linux.ibm.com>


On 21/01/2020 09:10, Tyrel Datwyler wrote:
> From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
> 
> 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:
> [c0000002879e39f0] [c00000000071ecb4] refcount_warn_saturate+0x184/0x190
> (unreliable)
> [c0000002879e3a50] [c0000000000500ac] iommu_tce_table_put+0x9c/0xb0
> [c0000002879e3a70] [c0000000000f54e4] vio_dev_release+0x34/0x70
> [c0000002879e3aa0] [c00000000087cfa4] device_release+0x54/0xf0
> [c0000002879e3b10] [c000000000d64c84] kobject_cleanup+0xa4/0x240
> [c0000002879e3b90] [c00000000087d358] put_device+0x28/0x40
> [c0000002879e3bb0] [c0000000007a328c] dlpar_remove_slot+0x15c/0x250
> [c0000002879e3c50] [c0000000007a348c] remove_slot_store+0xac/0xf0
> [c0000002879e3cd0] [c000000000d64220] kobj_attr_store+0x30/0x60
> [c0000002879e3cf0] [c0000000004ff13c] sysfs_kf_write+0x6c/0xa0
> [c0000002879e3d10] [c0000000004fde4c] kernfs_fop_write+0x18c/0x260
> [c0000002879e3d60] [c000000000410f3c] __vfs_write+0x3c/0x70
> [c0000002879e3d80] [c000000000415408] vfs_write+0xc8/0x250
> [c0000002879e3dd0] [c0000000004157dc] ksys_write+0x7c/0x120
> [c0000002879e3e20] [c00000000000b278] 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 <tyreld@linux.ibm.com>


Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>


> ---
>  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(&tbl->it_kref);
> +
>  	of_parse_dma_window(dev->dev.of_node, dma_window,
>  			    &tbl->it_index, &offset, &size);
>  
> 

-- 
Alexey