[PATCH net-next 07/15] batman-adv: bla: avoid negative reported BATADV_ATTR_LAST_SEEN_MSECS

[Simon Wunderlich <sw@simonwunderlich.de>]

From: Sven Eckelmann <sven@narfation.org>

To avoid an underflow due to an non-strict order read of jiffies vs
lasttime, use jiffies_delta_to_msecs instead of jiffies_to_msecs to
evaluate the delta.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/bridge_loop_avoidance.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index a96f269da8d37..0833f9f99e2a9 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -2363,6 +2363,7 @@ batadv_bla_backbone_dump_entry(struct sk_buff *msg, u32 portid,
 			       struct batadv_bla_backbone_gw *backbone_gw)
 {
 	const u8 *primary_addr = primary_if->net_dev->dev_addr;
+	unsigned long lasttime;
 	int ret = -EINVAL;
 	u16 backbone_crc;
 	bool is_own;
@@ -2385,7 +2386,8 @@ batadv_bla_backbone_dump_entry(struct sk_buff *msg, u32 portid,
 	backbone_crc = backbone_gw->crc;
 	spin_unlock_bh(&backbone_gw->crc_lock);
 
-	msecs = jiffies_to_msecs(jiffies - READ_ONCE(backbone_gw->lasttime));
+	lasttime = READ_ONCE(backbone_gw->lasttime);
+	msecs = jiffies_delta_to_msecs(jiffies - lasttime);
 
 	if (is_own)
 		if (nla_put_flag(msg, BATADV_ATTR_BLA_OWN)) {
-- 
2.47.3