Re: [syzbot] [net?] KASAN: use-after-free Read in __skb_flow_dissect (3)

[Hillf Danton]

On Mon, 01 Jan 2024 09:18:16 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    f5837722ffec Merge tag 'mm-hotfixes-stable-2023-12-27-15-0..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=122dfc65e80000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  master

--- x/net/core/filter.c
+++ y/net/core/filter.c
@@ -2161,6 +2161,10 @@ static int __bpf_redirect_no_mac(struct
 	}
 	skb_pop_mac_header(skb);
 	skb_reset_mac_len(skb);
+
+	if (skb->data[0] < 2)
+		flags = 0;
+
 	return flags & BPF_F_INGRESS ?
 	       __bpf_rx_skb_no_mac(dev, skb) : __bpf_tx_skb(dev, skb);
 }
--- x/net/ipv4/ipip.c
+++ y/net/ipv4/ipip.c
@@ -281,6 +281,9 @@ static netdev_tx_t ipip_tunnel_xmit(stru
 	if (!pskb_inet_may_pull(skb))
 		goto tx_error;
 
+	if (skb->data[0] < 2)
+		DEV_STATS_INC(dev, tx_errors);
+
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		ipproto = IPPROTO_IPIP;
@@ -302,6 +305,9 @@ static netdev_tx_t ipip_tunnel_xmit(stru
 
 	skb_set_inner_ipproto(skb, ipproto);
 
+	if (skb->data[0] < 2)
+		DEV_STATS_INC(dev, tx_errors);
+
 	if (tunnel->collect_md)
 		ip_md_tunnel_xmit(skb, dev, ipproto, 0);
 	else
--- x/net/ipv4/ip_tunnel.c
+++ y/net/ipv4/ip_tunnel.c
@@ -745,6 +745,9 @@ void ip_tunnel_xmit(struct sk_buff *skb,
 		}
 	}
 
+	if (skb->data[0] < 2)
+		DEV_STATS_INC(dev, tx_errors);
+
 	ip_tunnel_init_flow(&fl4, protocol, dst, tnl_params->saddr,
 			    tunnel->parms.o_key, RT_TOS(tos),
 			    dev_net(dev), tunnel->parms.link,
@@ -828,6 +831,9 @@ void ip_tunnel_xmit(struct sk_buff *skb,
 		return;
 	}
 
+	if (skb->data[0] < 2)
+		DEV_STATS_INC(dev, tx_errors);
+
 	iptunnel_xmit(NULL, rt, skb, fl4.saddr, fl4.daddr, protocol, tos, ttl,
 		      df, !net_eq(tunnel->net, dev_net(dev)));
 	return;
--