Re: [PATCH] virtio_balloon: prevent uninitialized variable use

[Denis V. Lunev]

On 03/23/2017 06:17 PM, Arnd Bergmann wrote:
> The latest gcc-7.0.1 snapshot reports a new warning:
>
> virtio/virtio_balloon.c: In function 'update_balloon_stats':
> virtio/virtio_balloon.c:258:26: error: 'events[2]' is used uninitialized in this function [-Werror=uninitialized]
> virtio/virtio_balloon.c:260:26: error: 'events[3]' is used uninitialized in this function [-Werror=uninitialized]
> virtio/virtio_balloon.c:261:56: error: 'events[18]' is used uninitialized in this function [-Werror=uninitialized]
> virtio/virtio_balloon.c:262:56: error: 'events[17]' is used uninitialized in this function [-Werror=uninitialized]
>
> This seems absolutely right, so we should add an extra check to
> prevent copying uninitialized stack data into the statistics.
> From all I can tell, this has been broken since the statistics code
> was originally added in 2.6.34.
>
> Fixes: 9564e138b1f6 ("virtio: Add memory statistics reporting to the balloon driver (V4)")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Reviewed-by: Denis V. Lunev <den@xxxxxxxxxx>



> ---
>  drivers/virtio/virtio_balloon.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 4e1191508228..cd5c54e2003d 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -254,12 +254,14 @@ static void update_balloon_stats(struct virtio_balloon *vb)
>  
>  	available = si_mem_available();
>  
> +#ifdef CONFIG_VM_EVENT_COUNTERS
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
>  				pages_to_bytes(events[PSWPIN]));
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
>  				pages_to_bytes(events[PSWPOUT]));
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
> +#endif
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
>  				pages_to_bytes(i.freeram));
>  	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,