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Message-Id: <20220408043341.416219-1-kevmitch@arista.com>
Date: Thu, 7 Apr 2022 21:33:40 -0700
From: Kevin Mitchell <kevmitch@...sta.com>
To: unlisted-recipients:; (no To-header on input)
Cc: kevmitch@...sta.com, gal@...dia.com,
Pablo Neira Ayuso <pablo@...filter.org>,
Jozsef Kadlecsik <kadlec@...filter.org>,
Florian Westphal <fw@...len.de>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
David Ahern <dsahern@...nel.org>,
netfilter-devel@...r.kernel.org, coreteam@...filter.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH nf-next v2 1/1] netfilter: conntrack: skip verification of zero UDP checksum
The checksum is optional for UDP packets in IPv4. However nf_reject
would previously require a valid checksum to elicit a response such as
ICMP_DEST_UNREACH.
Add some logic to nf_reject_verify_csum to determine if a UDP packet has
a zero checksum and should therefore not be verified. Explicitly require
a valid checksum for IPv6 consistent RFC 2460 and with the non-netfilter
stack (see udp6_csum_zero_error).
Signed-off-by: Kevin Mitchell <kevmitch@...sta.com>
---
include/net/netfilter/nf_reject.h | 27 +++++++++++++++++++++++----
net/ipv4/netfilter/nf_reject_ipv4.c | 10 +++++++---
net/ipv6/netfilter/nf_reject_ipv6.c | 4 ++--
3 files changed, 32 insertions(+), 9 deletions(-)
diff --git a/include/net/netfilter/nf_reject.h b/include/net/netfilter/nf_reject.h
index 9051c3a0c8e7..f248c1ff8b22 100644
--- a/include/net/netfilter/nf_reject.h
+++ b/include/net/netfilter/nf_reject.h
@@ -5,12 +5,34 @@
#include <linux/types.h>
#include <uapi/linux/in.h>
-static inline bool nf_reject_verify_csum(__u8 proto)
+static inline bool nf_reject_verify_csum(struct sk_buff *skb, int dataoff,
+ __u8 proto)
{
/* Skip protocols that don't use 16-bit one's complement checksum
* of the entire payload.
*/
switch (proto) {
+ /* Protocols with optional checksums. */
+ case IPPROTO_UDP: {
+ const struct udphdr *udp_hdr;
+ struct udphdr _udp_hdr;
+
+ /* Checksum is required in IPv6
+ * see RFC 2460 section 8.1
+ */
+ if (skb->protocol == htons(ETH_P_IPV6))
+ return true;
+
+ udp_hdr = skb_header_pointer(skb, dataoff,
+ sizeof(_udp_hdr),
+ &_udp_hdr);
+ if (!udp_hdr || udp_hdr->check)
+ return true;
+
+ return false;
+ }
+ case IPPROTO_GRE:
+
/* Protocols with other integrity checks. */
case IPPROTO_AH:
case IPPROTO_ESP:
@@ -19,9 +41,6 @@ static inline bool nf_reject_verify_csum(__u8 proto)
/* Protocols with partial checksums. */
case IPPROTO_UDPLITE:
case IPPROTO_DCCP:
-
- /* Protocols with optional checksums. */
- case IPPROTO_GRE:
return false;
}
return true;
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 4eed5afca392..6c46d4e8ab84 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -82,6 +82,7 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
unsigned int len;
__wsum csum;
u8 proto;
+ int dataoff;
if (!nf_reject_iphdr_validate(oldskb))
return NULL;
@@ -99,10 +100,11 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
return NULL;
+ dataoff = ip_hdrlen(oldskb);
proto = ip_hdr(oldskb)->protocol;
if (!skb_csum_unnecessary(oldskb) &&
- nf_reject_verify_csum(proto) &&
+ nf_reject_verify_csum(oldskb, dataoff, proto) &&
nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
return NULL;
@@ -312,6 +314,7 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
{
struct iphdr *iph = ip_hdr(skb_in);
u8 proto = iph->protocol;
+ int dataoff = ip_hdrlen(skb_in);
if (iph->frag_off & htons(IP_OFFSET))
return;
@@ -320,12 +323,13 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
nf_reject_fill_skb_dst(skb_in) < 0)
return;
- if (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
+ if (skb_csum_unnecessary(skb_in) ||
+ !nf_reject_verify_csum(skb_in, dataoff, proto)) {
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
return;
}
- if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
+ if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
}
EXPORT_SYMBOL_GPL(nf_send_unreach);
diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index dffeaaaadcde..f61d4f18e1cf 100644
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -31,7 +31,7 @@ static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
return false;
- if (!nf_reject_verify_csum(proto))
+ if (!nf_reject_verify_csum(skb, thoff, proto))
return true;
return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
@@ -388,7 +388,7 @@ static bool reject6_csum_ok(struct sk_buff *skb, int hook)
if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
return false;
- if (!nf_reject_verify_csum(proto))
+ if (!nf_reject_verify_csum(skb, thoff, proto))
return true;
return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
--
2.35.1
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