Re: [PATCH v2 1/3 for 9.2] hw/virtio: fix crash in processing balloon stats

[David Hildenbrand <david@redhat.com>]

On 29.11.24 14:55, Daniel P. Berrangé wrote:
> balloon_stats_get_all will iterate over guest stats upto the max
> VIRTIO_BALLOON_S_NR value, calling visit_type_uint64 to populate
> the QObject dict. The dict keys are obtained from the static
> array balloon_stat_names which is VIRTIO_BALLOON_S_NR in size.
> 
> Unfortunately the way that array is declared results in any
> unassigned stats getting a NULL name, which will then cause
> visit_type_uint64 to trigger an assert in qobject_output_add_obj.
> 
> The balloon_stat_names array was fortunately fully populated with
> names until recently:
> 
>    commit 0d2eeef77a33315187df8519491a900bde4a3d83
>    Author: Bibo Mao <maobibo@loongson.cn>
>    Date:   Mon Oct 28 10:38:09 2024 +0800
> 
>      linux-headers: Update to Linux v6.12-rc5
> 
> pulled a change to include/standard-headers/linux/virtio_balloon.h
> which increased VIRTIO_BALLOON_S_NR by 6, and failed to add the new
> names to balloon_stat_names.
> 
> This commit fills in the missing names, and uses a static assert to
> guarantee that any future changes to VIRTIO_BALLOON_S_NR will cause
> a build failure until balloon_stat_names is updated.
> 
> This problem was detected by the Cockpit Project's automated
> integration tests on QEMU 9.2.0-rc1.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2329448
> Fixes: 0d2eeef77a33315187df8519491a900bde4a3d83
> Reported-by: Martin Pitt <mpitt@redhat.com>
> Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
>   hw/virtio/virtio-balloon.c | 16 +++++++++++++++-
>   1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 609e39a821..afd2ad6dd6 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -167,19 +167,33 @@ static void balloon_deflate_page(VirtIOBalloon *balloon,
>       }
>   }
>   
> +/*
> + * All stats upto VIRTIO_BALLOON_S_NR /must/ have a
> + * non-NULL name declared here, since these are used
> + * as keys for populating the QDict with stats
> + */
>   static const char *balloon_stat_names[] = {
>      [VIRTIO_BALLOON_S_SWAP_IN] = "stat-swap-in",
>      [VIRTIO_BALLOON_S_SWAP_OUT] = "stat-swap-out",
>      [VIRTIO_BALLOON_S_MAJFLT] = "stat-major-faults",
>      [VIRTIO_BALLOON_S_MINFLT] = "stat-minor-faults",
>      [VIRTIO_BALLOON_S_MEMFREE] = "stat-free-memory",
> +
>      [VIRTIO_BALLOON_S_MEMTOT] = "stat-total-memory",
>      [VIRTIO_BALLOON_S_AVAIL] = "stat-available-memory",
>      [VIRTIO_BALLOON_S_CACHES] = "stat-disk-caches",
>      [VIRTIO_BALLOON_S_HTLB_PGALLOC] = "stat-htlb-pgalloc",
>      [VIRTIO_BALLOON_S_HTLB_PGFAIL] = "stat-htlb-pgfail",
> -   [VIRTIO_BALLOON_S_NR] = NULL
> +
> +   [VIRTIO_BALLOON_S_OOM_KILL] = "stat-oom-kills",
> +   [VIRTIO_BALLOON_S_ALLOC_STALL] = "stat-alloc-stalls",
> +   [VIRTIO_BALLOON_S_ASYNC_SCAN] = "stat-async-scans",
> +   [VIRTIO_BALLOON_S_DIRECT_SCAN] = "stat-direct-scans",
> +   [VIRTIO_BALLOON_S_ASYNC_RECLAIM] = "stat-async-reclaims",
> +
> +   [VIRTIO_BALLOON_S_DIRECT_RECLAIM] = "stat-direct-reclaims",
>   };
> +G_STATIC_ASSERT(G_N_ELEMENTS(balloon_stat_names) == VIRTIO_BALLOON_S_NR);
>   
>   /*
>    * reset_stats - Mark all items in the stats array as unset


Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb