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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Craig Gallek <kraig@google.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>
Subject: [PATCH 4.9 063/102] bpf: udp: ipv6: Avoid running reuseports bpf_prog from __udp6_lib_err
Date:   Mon,  8 Jul 2019 17:12:56 +0200
Message-Id: <20190708150529.714551171@linuxfoundation.org>
In-Reply-To: <20190708150525.973820964@linuxfoundation.org>
References: <20190708150525.973820964@linuxfoundation.org>
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From: Martin KaFai Lau <kafai@fb.com>

commit 4ac30c4b3659efac031818c418beb51e630d512d upstream.

__udp6_lib_err() may be called when handling icmpv6 message. For example,
the icmpv6 toobig(type=2).  __udp6_lib_lookup() is then called
which may call reuseport_select_sock().  reuseport_select_sock() will
call into a bpf_prog (if there is one).

reuseport_select_sock() is expecting the skb->data pointing to the
transport header (udphdr in this case).  For example, run_bpf_filter()
is pulling the transport header.

However, in the __udp6_lib_err() path, the skb->data is pointing to the
ipv6hdr instead of the udphdr.

One option is to pull and push the ipv6hdr in __udp6_lib_err().
Instead of doing this, this patch follows how the original
commit 538950a1b752 ("soreuseport: setsockopt SO_ATTACH_REUSEPORT_[CE]BPF")
was done in IPv4, which has passed a NULL skb pointer to
reuseport_select_sock().

Fixes: 538950a1b752 ("soreuseport: setsockopt SO_ATTACH_REUSEPORT_[CE]BPF")
Cc: Craig Gallek <kraig@google.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Craig Gallek <kraig@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/udp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -479,7 +479,7 @@ void __udp6_lib_err(struct sk_buff *skb,
 	struct net *net = dev_net(skb->dev);
 
 	sk = __udp6_lib_lookup(net, daddr, uh->dest, saddr, uh->source,
-			       inet6_iif(skb), udptable, skb);
+			       inet6_iif(skb), udptable, NULL);
 	if (!sk) {
 		__ICMP6_INC_STATS(net, __in6_dev_get(skb->dev),
 				  ICMP6_MIB_INERRORS);