icmp: fix icmp_ndo_send address translation for reply direction

JIRA: https://issues.redhat.com/browse/RHEL-115578

commit c6dd1aa
Author: Fabian Bläse <fabian@blaese.de>
Date:   Thu Aug 28 11:14:35 2025 +0200

    icmp: fix icmp_ndo_send address translation for reply direction

    The icmp_ndo_send function was originally introduced to ensure proper
    rate limiting when icmp_send is called by a network device driver,
    where the packet's source address may have already been transformed
    by SNAT.

    However, the original implementation only considers the
    IP_CT_DIR_ORIGINAL direction for SNAT and always replaced the packet's
    source address with that of the original-direction tuple. This causes
    two problems:

    1. For SNAT:
       Reply-direction packets were incorrectly translated using the source
       address of the CT original direction, even though no translation is
       required.

    2. For DNAT:
       Reply-direction packets were not handled at all. In DNAT, the original
       direction's destination is translated. Therefore, in the reply
       direction the source address must be set to the reply-direction
       source, so rate limiting works as intended.

    Fix this by using the connection direction to select the correct tuple
    for source address translation, and adjust the pre-checks to handle
    reply-direction packets in case of DNAT.

    Additionally, wrap the `ct->status` access in READ_ONCE(). This avoids
    possible KCSAN reports about concurrent updates to `ct->status`.

    Fixes: 0b41713 ("icmp: introduce helper for nat'd source address in network device context")
    Signed-off-by: Fabian Bläse <fabian@blaese.de>
    Cc: Jason A. Donenfeld <Jason@zx2c4.com>
    Reviewed-by: Florian Westphal <fw@strlen.de>
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/ipv4/icmp.c

@@ -801,11 +801,12 @@ void icmp_ndo_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 	struct sk_buff *cloned_skb = NULL;
 	struct ip_options opts = { 0 };
 	enum ip_conntrack_info ctinfo;
+	enum ip_conntrack_dir dir;
 	struct nf_conn *ct;
 	__be32 orig_ip;
 
 	ct = nf_ct_get(skb_in, &ctinfo);
-	if (!ct || !(ct->status & IPS_SRC_NAT)) {
+	if (!ct || !(READ_ONCE(ct->status) & IPS_NAT_MASK)) {
 		__icmp_send(skb_in, type, code, info, &opts);
 		return;
 	}
@@ -820,7 +821,8 @@ void icmp_ndo_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 		goto out;
 
 	orig_ip = ip_hdr(skb_in)->saddr;
-	ip_hdr(skb_in)->saddr = ct->tuplehash[0].tuple.src.u3.ip;
+	dir = CTINFO2DIR(ctinfo);
+	ip_hdr(skb_in)->saddr = ct->tuplehash[dir].tuple.src.u3.ip;
 	__icmp_send(skb_in, type, code, info, &opts);
 	ip_hdr(skb_in)->saddr = orig_ip;
 out:

net/ipv6/ip6_icmp.c

@@ -54,11 +54,12 @@ void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
 	struct inet6_skb_parm parm = { 0 };
 	struct sk_buff *cloned_skb = NULL;
 	enum ip_conntrack_info ctinfo;
+	enum ip_conntrack_dir dir;
 	struct in6_addr orig_ip;
 	struct nf_conn *ct;
 
 	ct = nf_ct_get(skb_in, &ctinfo);
-	if (!ct || !(ct->status & IPS_SRC_NAT)) {
+	if (!ct || !(READ_ONCE(ct->status) & IPS_NAT_MASK)) {
 		__icmpv6_send(skb_in, type, code, info, &parm);
 		return;
 	}
@@ -73,7 +74,8 @@ void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
 		goto out;
 
 	orig_ip = ipv6_hdr(skb_in)->saddr;
-	ipv6_hdr(skb_in)->saddr = ct->tuplehash[0].tuple.src.u3.in6;
+	dir = CTINFO2DIR(ctinfo);
+	ipv6_hdr(skb_in)->saddr = ct->tuplehash[dir].tuple.src.u3.in6;
 	__icmpv6_send(skb_in, type, code, info, &parm);
 	ipv6_hdr(skb_in)->saddr = orig_ip;
 out: