Re: [syzbot] [netfilter?] KASAN: slab-use-after-free Read in ip_skb_dst_mtu

[Hillf Danton]

On Wed, 06 Mar 2024 02:57:18 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    805d849d7c3c Merge tag 'acpi-6.8-rc7' of git://git.kernel...
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1025fa6a180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fe46a7dd189e

--- x/drivers/net/ipvlan/ipvlan_core.c
+++ y/drivers/net/ipvlan/ipvlan_core.c
@@ -426,6 +426,7 @@ static noinline_for_stack int ipvlan_pro
 		.daddr = ip4h->daddr,
 		.saddr = ip4h->saddr,
 	};
+	struct sock *sk;
 
 	rt = ip_route_output_flow(net, &fl4, NULL);
 	if (IS_ERR(rt))
@@ -439,7 +440,12 @@ static noinline_for_stack int ipvlan_pro
 
 	memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
 
+	sk = skb->sk;
+	if (!sk)
+		goto err;
+	refcount_inc(&sk->sk_wmem_alloc);
 	err = ip_local_out(net, skb->sk, skb);
+	sk_free(sk);
 	if (unlikely(net_xmit_eval(err)))
 		DEV_STATS_INC(dev, tx_errors);
 	else
--