[libvirt] [PATCH] qemu: qapi: Limit traversal depth for QAPI schema queries

[Daniel P. Berrangé]

On Fri, Sep 06, 2019 at 10:33:15AM +0200, Peter Krempa wrote:
> Implicitly the query depth is limited by the length of the QAPI schema
> query, but 'alternate' and 'array' QAPI meta-types don't consume a part
> of the query string thus a loop on such types would get our traversal
> code stuck in an infinite loop. Prevent this from happening by limiting
> the nesting depth to 1000.

I'm not too clear on what 'depth' is applying to here ? Is this
the level of nesting in the JSON compound types we're following,
or is it something else ?

I ask because YAJL limits JSON nesting to only 128. So 1000 is
almost an order of magnitude larger.

> 
> Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> ---
>  src/qemu/qemu_qapi.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/src/qemu/qemu_qapi.c b/src/qemu/qemu_qapi.c
> index 0226d6c659..93fcae0d44 100644
> --- a/src/qemu/qemu_qapi.c
> +++ b/src/qemu/qemu_qapi.c
> @@ -74,9 +74,23 @@ struct virQEMUQAPISchemaTraverseContext {
>      virHashTablePtr schema;
>      char **queries;
>      virJSONValuePtr returnType;
> +    size_t depth;
>  };
> 
> 
> +static int
> +virQEMUQAPISchemaTraverseContextValidateDepth(struct virQEMUQAPISchemaTraverseContext *ctxt)
> +{
> +    if (ctxt->depth++ > 1000) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                       _("possible loop in QMP schema"));
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +
>  static void
>  virQEMUQAPISchemaTraverseContextInit(struct virQEMUQAPISchemaTraverseContext *ctxt,
>                                       char **queries,
> @@ -329,6 +343,9 @@ virQEMUQAPISchemaTraverse(const char *baseName,
>      const char *metatype;
>      size_t i;
> 
> +    if (virQEMUQAPISchemaTraverseContextValidateDepth(ctxt) < 0)
> +        return -2;
> +
>      if (!(cur = virHashLookup(ctxt->schema, baseName)))
>          return -2;
> 
> -- 
> 2.21.0
> 
> --
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Regards,
Daniel
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