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From: Hillf Danton <hdanton@sina.com>
To: syzbot <syzbot+e5167d7144a62715044c@syzkaller.appspotmail.com>
Cc: linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [netfilter?] KASAN: slab-use-after-free Read in ip_skb_dst_mtu
Date: Sat,  9 Mar 2024 16:45:27 +0800
Message-Id: <20240309084527.1943-1-hdanton@sina.com>
In-Reply-To: <0000000000008b9c410612fbd266@google.com>
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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://github.com/fbq/linux.git  rcu-exp.2024.01.29b

--- 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
--