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

["Richard W.M. Jones" <rjones@redhat.com>]

On Fri, Nov 29, 2024 at 09:45:51AM +0000, 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: 0d2eeef77a33315187df8519491a900bde4a3d83
> Reported-by: Martin Pitt <mpitt@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

You probably want to have a link to the original bug report for context:

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2329448

Rich.

> ---
> 
> NB: this is a MUST FIX for 9.2, as a trivial guest triggerable crash
> regressing since 9.1
> 
>  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
> -- 
> 2.46.0

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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