net: bonding: fix use-after-free after 802.3ad slave unbind

commit 0622cab0 ("bonding: fix 802.3ad aggregator reselection"),
resolve case, when there is several aggregation groups in the same bond.
bond_3ad_unbind_slave will invalidate (clear) aggregator when
__agg_active_ports return zero. So, ad_clear_agg can be executed even, when
num_of_ports!=0. Than bond_3ad_unbind_slave can be executed again for,
previously cleared aggregator. NOTE: at this time bond_3ad_unbind_slave
will not update slave ports list, because lag_ports==NULL. So, here we
got slave ports, pointing to freed aggregator memory.

Fix with checking actual number of ports in group (as was before
commit 0622cab0 ("bonding: fix 802.3ad aggregator reselection") ),
before ad_clear_agg().

The KASAN logs are as follows:

[  767.617392] ==================================================================
[  767.630776] BUG: KASAN: use-after-free in bond_3ad_state_machine_handler+0x13dc/0x1470
[  767.638764] Read of size 2 at addr ffff00011ba9d430 by task kworker/u8:7/767
[  767.647361] CPU: 3 PID: 767 Comm: kworker/u8:7 Tainted: G           O 5.15.11 #15
[  767.655329] Hardware name: DNI AmazonGo1 A7040 board (DT)
[  767.660760] Workqueue: lacp_1 bond_3ad_state_machine_handler
[  767.666468] Call trace:
[  767.668930]  dump_backtrace+0x0/0x2d0
[  767.672625]  show_stack+0x24/0x30
[  767.675965]  dump_stack_lvl+0x68/0x84
[  767.679659]  print_address_description.constprop.0+0x74/0x2b8
[  767.685451]  kasan_report+0x1f0/0x260
[  767.689148]  __asan_load2+0x94/0xd0
[  767.692667]  bond_3ad_state_machine_handler+0x13dc/0x1470

Fixes: 0622cab0 ("bonding: fix 802.3ad aggregator reselection")
Co-developed-by: Maksym Glubokiy <maksym.glubokiy@plvision.eu>
Signed-off-by: Maksym Glubokiy <maksym.glubokiy@plvision.eu>
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Link: https://lore.kernel.org/r/20220629012914.361-1-yevhen.orlov@plvision.euSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/bonding/bond_3ad.c

@@ -2228,7 +2228,8 @@ void bond_3ad_unbind_slave(struct slave *slave)
 				temp_aggregator->num_of_ports--;
 				if (__agg_active_ports(temp_aggregator) == 0) {
 					select_new_active_agg = temp_aggregator->is_active;
-					ad_clear_agg(temp_aggregator);
+					if (temp_aggregator->num_of_ports == 0)
+						ad_clear_agg(temp_aggregator);
 					if (select_new_active_agg) {
 						slave_info(bond->dev, slave->dev, "Removing an active aggregator\n");
 						/* select new active aggregator */