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    Subject[PATCH 4.4 062/193] virtio_balloon: prevent uninitialized variable use
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Arnd Bergmann <arnd@arndb.de>

    commit f0bb2d50dfcc519f06f901aac88502be6ff1df2c upstream.

    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@arndb.de>
    Signed-off-by: Ladi Prosek <lprosek@redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/virtio/virtio_balloon.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/drivers/virtio/virtio_balloon.c
    +++ b/drivers/virtio/virtio_balloon.c
    @@ -239,12 +239,14 @@ static void update_balloon_stats(struct
    all_vm_events(events);
    si_meminfo(&i);

    +#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,

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