[B.A.T.M.A.N.] [PATCH 1/2] batman-adv: Avoid u32 overflow during gateway select

Antonio Quartulli
2015-06-16T19:06:23Z

From: Ruben Wisniewski <ruben@freifunk-nrw.de>

The gateway selection based on fast connections is using a single value
calculated from the average tq (0-255) and the download bandwidth (in
100Kibit). The formula for the first step (tq ** 2 * 10000 * bandwidth)
tends to overflow a u32 with low bandwidth settings like 50 [100KiBit]
and a tq value of over 92.

Changing this to a 64 bit unsigned integer allows to support a
bandwidth_down with up to ~2.8e10 [100KiBit] and a perfect tq of 255. This
is ~6.6 times higher than the maximum possible value of the gateway
announcement TVLV.

This problem only affects the non-default gw_sel_class 1.

Signed-off-by: Ruben Wisniewsi <ruben@vfn-nrw.de>
[sven@narfation.org: rewritten commit message, changed to kernel type]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>

Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
---
net/batman-adv/gateway_client.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index 090828c..ca734f8 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -133,7 +133,7 @@ batadv_gw_get_best_gw_node(struct batadv_priv *bat_priv)
struct batadv_neigh_node *router;
struct batadv_neigh_ifinfo *router_ifinfo;
struct batadv_gw_node *gw_node, *curr_gw = NULL;
- uint32_t max_gw_factor = 0, tmp_gw_factor = 0;
+ uint64_t max_gw_factor = 0, tmp_gw_factor = 0;
uint32_t gw_divisor;
uint8_t max_tq = 0;
uint8_t tq_avg;
--
2.4.3