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: 0b41713b6066 ("icmp: introduce helper for nat'd source address in network device context") Signed-off-by: Fabian Bläse Cc: Jason A. Donenfeld Cc: Florian Westphal --- Changes v1->v2: - Implement fix for ICMPv6 as well Changes v2->v3: - Collapse conditional tuple selection into a single direction lookup [Florian] - Always apply source address translation if IPS_NAT_MASK is set [Florian] - Wrap ct->status in READ_ONCE() - Add a clearer explanation of the behaviour change for DNAT --- net/ipv4/icmp.c | 6 ++++-- net/ipv6/ip6_icmp.c | 6 ++++-- 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c index 2ffe73ea644f..c48c572f024d 100644 --- a/net/ipv4/icmp.c +++ b/net/ipv4/icmp.c @@ -799,11 +799,12 @@ 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; } @@ -818,7 +819,8 @@ 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: diff --git a/net/ipv6/ip6_icmp.c b/net/ipv6/ip6_icmp.c index 9e3574880cb0..233914b63bdb 100644 --- a/net/ipv6/ip6_icmp.c +++ b/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: -- 2.51.0