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Date:   Mon, 17 Dec 2018 16:24:21 +0100
From:   Stefano Brivio <sbrivio@redhat.com>
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        syzbot <syzbot+43f6755d1c2e62743468@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Josh Triplett <josh@joshtriplett.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        netdev <netdev@vger.kernel.org>
Subject: Re: WARNING in __rcu_read_unlock
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On Mon, 17 Dec 2018 06:57:35 -0800
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Might be cause by commit b8a51b38e4d4dec3e379d52c0fe1a66827f7cf1e
> fou, fou6: ICMP error handlers for FoU and GUE

This:

diff --git a/net/ipv4/fou.c b/net/ipv4/fou.c
index 0d0ad19ecb87..20a6de26d146 100644
--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -1008,6 +1008,9 @@ static int gue_err_proto_handler(int proto, struct sk_buff *skb, u32 info)
 {
        const struct net_protocol *ipprot = rcu_dereference(inet_protos[proto]);
 
+       if (ipprot == IPPROTO_UDP)
+               return -EINVAL;
+
        if (ipprot && ipprot->err_handler) {
                if (!ipprot->err_handler(skb, info))
                        return 0;

should fix the issue, but I still have to run tests and make sure we
don't hit similar cases.

-- 
Stefano