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    Subject[PATCH 5.5 072/120] powerpc/pseries/vio: Fix iommu_table use-after-free refcount warning
    Date
    From: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>

    commit aff8c8242bc638ba57247ae1ec5f272ac3ed3b92 upstream.

    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>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/1579558202-26052-1-git-send-email-tyreld@linux.ibm.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/platforms/pseries/vio.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/arch/powerpc/platforms/pseries/vio.c
    +++ b/arch/powerpc/platforms/pseries/vio.c
    @@ -1176,6 +1176,8 @@ static struct iommu_table *vio_build_iom
    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);


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