linux-kernel - [PATCH 5.1 49/55] bpf: udp: ipv6: Avoid running reuseports bpf_prog from __udp6_lib

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Message-Id: <20190702080126.622025751@linuxfoundation.org>
Date:   Tue,  2 Jul 2019 10:01:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Craig Gallek <kraig@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: [PATCH 5.1 49/55] bpf: udp: ipv6: Avoid running reuseports bpf_prog from __udp6_lib_err

From: Martin KaFai Lau <kafai@...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@...gle.com>
Signed-off-by: Martin KaFai Lau <kafai@...com>
Acked-by: Song Liu <songliubraving@...com>
Acked-by: Craig Gallek <kraig@...gle.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ipv6/udp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -520,7 +520,7 @@ int __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), inet6_sdif(skb), udptable, skb);
+			       inet6_iif(skb), inet6_sdif(skb), udptable, NULL);
 	if (!sk) {
 		/* No socket for error: try tunnels before discarding */
 		sk = ERR_PTR(-ENOENT);