Re: [Qemu-devel] [PATCH v2] hostmem: fix crash when querying empty host-nodes property via QMP

[Eric Blake <eblake@redhat.com>]

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On 2/14/19 4:57 AM, Igor Mammedov wrote:
> QEMU will crashes with
>  qapi/qobject-output-visitor.c:210: qobject_output_complete: Assertion `qov->root && ((&qov->stack)->slh_first == ((void *)0))' failed
> when trying to get value of not set hostmem's "host-nodes"
> property, HostMemoryBackend::host_nodes bitmap doesn't have
> any bits set in it, which leads to find_first_bit() returning
> MAX_NODES and consequently to an early return from
> host_memory_backend_get_host_nodes() without calling visitor.
> 
> Fix it by calling visitor even if "host-nodes" property wasn't
> set before exiting from property getter to return valid empty
> list.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> v2:
>   * fixup commit message to put emphasis on property instead
>     local variable host_nodes and make explanation more hopefully
>     more clear. (Markus Armbruster <armbru@redhat.com>)
> ---
>  backends/hostmem.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

> diff --git a/backends/hostmem.c b/backends/hostmem.c
> index 87b19d2111..04baf479a1 100644
> --- a/backends/hostmem.c
> +++ b/backends/hostmem.c
> @@ -88,7 +88,7 @@ host_memory_backend_get_host_nodes(Object *obj, Visitor *v, const char *name,
>  
>      value = find_first_bit(backend->host_nodes, MAX_NODES);
>      if (value == MAX_NODES) {
> -        return;
> +        goto ret;
>      }
>  
>      *node = g_malloc0(sizeof(**node));
> @@ -106,6 +106,7 @@ host_memory_backend_get_host_nodes(Object *obj, Visitor *v, const char *name,
>          node = &(*node)->next;
>      } while (true);
>  
> +ret:
>      visit_type_uint16List(v, name, &host_nodes, errp);
>  }
>  
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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