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

[Michael Ellerman]

On Mon, 2020-01-20 at 22:10:02 UTC, Tyrel Datwyler wrote:
> From: Tyrel Datwyler <tyreld at 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 at linux.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/aff8c8242bc638ba57247ae1ec5f272ac3ed3b92

cheers