Re: [Xen-devel] [PATCH for-4.13] xen/xsm: flask: Prevent NULL deference in flask_assign_{, dt}device()

[Paul Durrant <pdurrant@xxxxxxxxx>]

On Fri, 4 Oct 2019 at 17:42, Julien Grall <julien.grall@xxxxxxx> wrote:
>
> flask_assign_{, dt}device() may be used to check whether you can test if
> a device is assigned. In this case, the domain will be NULL.
>
> However, flask_iommu_resource_use_perm() will be called and may end up
> to deference a NULL pointer. This can be prevented by moving the call
> after we check the validity for the domain pointer.
>
> Coverity-ID: 1486741
> Fixes: 71e617a6b8 ('use is_iommu_enabled() where appropriate...')
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Paul Durrant <paul@xxxxxxx>

> ---
>  xen/xsm/flask/hooks.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
> index 3b30827764..cf7f25cda2 100644
> --- a/xen/xsm/flask/hooks.c
> +++ b/xen/xsm/flask/hooks.c
> @@ -1296,11 +1296,13 @@ static int flask_assign_device(struct domain *d, 
> uint32_t machine_bdf)
>      u32 dsid, rsid;
>      int rc = -EPERM;
>      struct avc_audit_data ad;
> -    u32 dperm = flask_iommu_resource_use_perm(d);
> +    u32 dperm;
>
>      if ( !d )
>          return flask_test_assign_device(machine_bdf);
>
> +    dperm = flask_iommu_resource_use_perm(d);
> +
>      rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
>      if ( rc )
>          return rc;
> @@ -1355,11 +1357,13 @@ static int flask_assign_dtdevice(struct domain *d, 
> const char *dtpath)
>      u32 dsid, rsid;
>      int rc = -EPERM;
>      struct avc_audit_data ad;
> -    u32 dperm = flask_iommu_resource_use_perm(d);
> +    u32 dperm;
>
>      if ( !d )
>          return flask_test_assign_dtdevice(dtpath);
>
> +    dperm = flask_iommu_resource_use_perm(d);
> +
>      rc = current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__ADD);
>      if ( rc )
>          return rc;
> --
> 2.11.0
>

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