From: Kevin Mitchell <kevmitch@arista•com>
To: unlisted-recipients:; (no To-header on input)
Cc: kevmitch@arista•com, Pablo Neira Ayuso <pablo@netfilter•org>,
Jozsef Kadlecsik <kadlec@netfilter•org>,
Florian Westphal <fw@strlen•de>,
"David S. Miller" <davem@davemloft•net>,
Jakub Kicinski <kuba@kernel•org>,
netfilter-devel@vger•kernel.org, coreteam@netfilter•org,
netdev@vger•kernel.org, linux-kernel@vger•kernel.org
Subject: [PATCH 1/1] netfilter: conntrack: mark UDP zero checksum as CHECKSUM_UNNECESSARY
Date: Fri, 14 Jan 2022 20:00:50 -0800 [thread overview]
Message-ID: <20220115040050.187972-2-kevmitch@arista.com> (raw)
In-Reply-To: <20220115040050.187972-1-kevmitch@arista.com>
The udp_error function verifies the checksum of incoming UDP packets if
one is set. This has the desirable side effect of setting skb->ip_summed
to CHECKSUM_COMPLETE, signalling that this verification need not be
repeated further up the stack.
Conversely, when the UDP checksum is empty, which is perfectly legal (at least
inside IPv4), udp_error previously left no trace that the checksum had been
deemed acceptable.
This was a problem in particular for nf_reject_ipv4, which verifies the
checksum in nf_send_unreach() before sending ICMP_DEST_UNREACH. It makes
no accommodation for zero UDP checksums unless they are already marked
as CHECKSUM_UNNECESSARY.
This commit ensures packets with empty UDP checksum are marked as
CHECKSUM_UNNECESSARY, which is explicitly recommended in skbuff.h.
Signed-off-by: Kevin Mitchell <kevmitch@arista•com>
---
net/netfilter/nf_conntrack_proto_udp.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/netfilter/nf_conntrack_proto_udp.c b/net/netfilter/nf_conntrack_proto_udp.c
index 3b516cffc779..12f793d8fe0c 100644
--- a/net/netfilter/nf_conntrack_proto_udp.c
+++ b/net/netfilter/nf_conntrack_proto_udp.c
@@ -63,8 +63,10 @@ static bool udp_error(struct sk_buff *skb,
}
/* Packet with no checksum */
- if (!hdr->check)
+ if (!hdr->check) {
+ skb->ip_summed = CHECKSUM_UNNECESSARY;
return false;
+ }
/* Checksum invalid? Ignore.
* We skip checking packets on the outgoing path
--
2.34.1
next prev parent reply other threads:[~2022-01-15 4:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-15 4:00 [PATCH 0/1] UDP traceroute packets with no checksum Kevin Mitchell
2022-01-15 4:00 ` Kevin Mitchell [this message]
2022-01-15 14:39 ` [PATCH 1/1] netfilter: conntrack: mark UDP zero checksum as CHECKSUM_UNNECESSARY Florian Westphal
2022-02-04 5:09 ` Pablo Neira Ayuso
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