[PATCH 5.10 13/23] batman-adv: frag: avoid underflow of TTL

[Sven Eckelmann <sven@narfation.org>]

commit 493d9d2528e1a09b090e4b37f0f553def7bd5ce9 upstream.

Packets with a TTL are using it to limit the amount of time this packet can
be forwarded. But for batadv_frag_packet, the TTL was always only reduced
but it was never evaluated. It could even underflow without any effect.

Check the TTL in batadv_frag_skb_fwd() before attempting to prepare it for
forwarding. This keeps it in sync with the not fragmented unicast packet.

Cc: stable@kernel.org
Fixes: 610bfc6bc99b ("batman-adv: Receive fragmented packets and merge")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/fragmentation.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 95c88bbdbcbee..43dfe86f07a9b 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -421,6 +421,13 @@ bool batadv_frag_skb_fwd(struct sk_buff *skb,
 	 */
 	total_size = ntohs(packet->total_size);
 	if (total_size > neigh_node->if_incoming->net_dev->mtu) {
+		if (packet->ttl < 2) {
+			kfree_skb(skb);
+			*rx_result = NET_RX_DROP;
+			ret = true;
+			goto out;
+		}
+
 		if (skb_cow(skb, ETH_HLEN) < 0) {
 			kfree_skb(skb);
 			*rx_result = NET_RX_DROP;
-- 
2.47.3