Re: [PATCH v3 1/5] batman-adv: Do not send uninitialized TT changes

[Remi Pommarel <repk@triplefau.lt>]

On Thu, Nov 21, 2024 at 02:05:58PM +0100, Antonio Quartulli wrote:
> On 20/11/2024 18:47, Remi Pommarel wrote:
> > The number of TT changes can be less than initially expected in
> > batadv_tt_tvlv_container_update() (changes can be removed by
> > batadv_tt_local_event() in ADD+DEL sequence between reading
> > tt_diff_entries_num and actually iterating the change list under lock).
> > 
> > Thus tt_diff_len could be bigger than the actual changes size that need
> > to be sent. Because batadv_send_my_tt_response sends the whole
> > packet, uninitialized data can be interpreted as TT changes on other
> > nodes leading to weird TT global entries on those nodes such as:
> > 
> >   * 00:00:00:00:00:00   -1 [....] (  0) 88:12:4e:ad:7e:ba (179) (0x45845380)
> >   * 00:00:00:00:78:79 4092 [.W..] (  0) 88:12:4e:ad:7e:3c (145) (0x8ebadb8b)
> > 
> > All of the above also applies to OGM tvlv container buffer's tvlv_len.
> > 
> > Remove the extra allocated space to avoid sending uninitialized TT
> > changes in batadv_send_my_tt_response() and batadv_v_ogm_send_softif().
> > 
> > Fixes: e1bf0c14096f ("batman-adv: tvlv - convert tt data sent within OGMs")
> > Signed-off-by: Remi Pommarel <repk@triplefau.lt>
> > ---
> >   net/batman-adv/translation-table.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> > 
> > diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
> > index 2243cec18ecc..f0590f9bc2b1 100644
> > --- a/net/batman-adv/translation-table.c
> > +++ b/net/batman-adv/translation-table.c
> > @@ -990,6 +990,7 @@ static void batadv_tt_tvlv_container_update(struct batadv_priv *bat_priv)
> >   	int tt_diff_len, tt_change_len = 0;
> >   	int tt_diff_entries_num = 0;
> >   	int tt_diff_entries_count = 0;
> > +	size_t tt_extra_len = 0;
> >   	u16 tvlv_len;
> >   	tt_diff_entries_num = atomic_read(&bat_priv->tt.local_changes);
> > @@ -1027,6 +1028,9 @@ static void batadv_tt_tvlv_container_update(struct batadv_priv *bat_priv)
> >   	}
> >   	spin_unlock_bh(&bat_priv->tt.changes_list_lock);
> 
> what speaks against acquiring tt.changes_list_lock before reading
> tt.local_changes? (and making sure the writer does the update under lock
> too) Any reason for not pursuing that path?

Nothing against, just tried to follow old behavior in case this was
that way for performance reasons. That would mean
batadv_tt_local_commit_changes_nolock() to take the lock; because it
is only called once per OGM interval I think that would be ok.

And now that I've looked into batadv_tt_tvlv_container_update() a bit
deeper I realize that it calls batadv_tt_prepare_tvlv_local_data() every
time, traversing the softif_vlan_list and building the tvlv container
over and over even if no changes occured (I mean even after the two OGM
that repeat last changes in case the first one has been lost).

Using lock for consistency maybe I can try to avoid that also ?

Thanks,

-- 
Remi