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icmp: fix icmp_ndo_send address translation for reply direction

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[ Upstream commit c6dd1aa2cbb72b33e0569f3e71d95792beab5042 ]

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 <[email protected]>
Cc: Jason A. Donenfeld <[email protected]>
Reviewed-by: Florian Westphal <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Fabian Bläse 2025-08-28 11:14:35 +02:00 • committed by Greg Kroah-Hartman
commit 8937d2fea1
2 changed files with 8 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

6
net/ipv6/ip6_icmp.c
View file

@ -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: