bonding: validate ip header before check IPPROTO_IGMP

[ Upstream commit 9d1bc24b ]

bond_xmit_roundrobin() checks for IGMP packets but it parses
the IP header even before checking skb->protocol.

We should validate the IP header with pskb_may_pull() before
using iph->protocol.

Reported-and-tested-by: syzbot+e5be16aa39ad6e755391@syzkaller.appspotmail.com
Fixes: a2fd940f ("bonding: fix broken multicast with round-robin mode")
Cc: Jay Vosburgh <j.vosburgh@gmail.com>
Cc: Veaceslav Falico <vfalico@gmail.com>
Cc: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/bonding/bond_main.c

@@ -3866,8 +3866,8 @@ static netdev_tx_t bond_xmit_roundrobin(struct sk_buff *skb,
 					struct net_device *bond_dev)
 {
 	struct bonding *bond = netdev_priv(bond_dev);
-	struct iphdr *iph = ip_hdr(skb);
 	struct slave *slave;
+	int slave_cnt;
 	u32 slave_id;
 
 	/* Start with the curr_active_slave that joined the bond as the
@@ -3876,23 +3876,32 @@ static netdev_tx_t bond_xmit_roundrobin(struct sk_buff *skb,
 	 * send the join/membership reports.  The curr_active_slave found
 	 * will send all of this type of traffic.
 	 */
-	if (iph->protocol == IPPROTO_IGMP && skb->protocol == htons(ETH_P_IP)) {
+	if (skb->protocol == htons(ETH_P_IP)) {
+		int noff = skb_network_offset(skb);
+		struct iphdr *iph;
+
+		if (unlikely(!pskb_may_pull(skb, noff + sizeof(*iph))))
+			goto non_igmp;
+
+		iph = ip_hdr(skb);
+		if (iph->protocol == IPPROTO_IGMP) {
 			slave = rcu_dereference(bond->curr_active_slave);
 			if (slave)
 				bond_dev_queue_xmit(bond, skb, slave->dev);
 			else
 				bond_xmit_slave_id(bond, skb, 0);
-	} else {
-		int slave_cnt = READ_ONCE(bond->slave_cnt);
+			return NETDEV_TX_OK;
+		}
+	}
 
+non_igmp:
+	slave_cnt = READ_ONCE(bond->slave_cnt);
 	if (likely(slave_cnt)) {
 		slave_id = bond_rr_gen_slave_id(bond);
 		bond_xmit_slave_id(bond, skb, slave_id % slave_cnt);
 	} else {
 		bond_tx_drop(bond_dev, skb);
 	}
-	}
-
 	return NETDEV_TX_OK;
 }