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([2a0d:3344:5521:6b10:2eb7:f61a:75:4534]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-493b8c79baasm72553465e9.7.2026.06.30.06.44.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Jun 2026 06:44:53 -0700 (PDT) Message-ID: Date: Tue, 30 Jun 2026 15:44:52 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] net/sched: act_nat: only rewrite IPv4 packets To: Samuel Moelius , Jamal Hadi Salim Cc: Jiri Pirko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , Herbert Xu , "open list:TC subsystem" , open list References: <20260628132029.2209612.f2aaf6467355.act-nat-non-ipv4@trailofbits.com> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260628132029.2209612.f2aaf6467355.act-nat-non-ipv4@trailofbits.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/28/26 3:20 PM, Samuel Moelius wrote: > act_nat can process packets whose protocol is not IPv4 and then > interpret the payload as an IPv4 header. Non-IPv4 packets may be > modified based on unrelated bytes at the network header offset. > > The action is documented as IPv4 NAT and should leave other protocols > alone. > > Check skb->protocol before parsing and rewriting the IPv4 header. This > keeps accepting hardware-accelerated VLAN IPv4 packets whose network > header already points at the IPv4 header, while still rejecting inline > VLAN packets because act_nat does not adjust the network header offset > before using ip_hdr(skb). > > Fixes: b4219952356b ("[PKT_SCHED]: Add stateless NAT") > Assisted-by: Codex:gpt-5.5-cyber-preview > Signed-off-by: Samuel Moelius > --- > Changes in v3: > - Check skb->protocol > Changes in v2: > - Check skb_protocol(skb, false) > > net/sched/act_nat.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/net/sched/act_nat.c b/net/sched/act_nat.c > index abb332dee836..1bf4a5853617 100644 > --- a/net/sched/act_nat.c > +++ b/net/sched/act_nat.c > @@ -142,6 +142,9 @@ TC_INDIRECT_SCOPE int tcf_nat_act(struct sk_buff *skb, > egress = parms->flags & TCA_NAT_FLAG_EGRESS; > > noff = skb_network_offset(skb); > + if (skb->protocol != htons(ETH_P_IP)) AFAICS, in the xmit path, for actions applied at the H/W NIC level, without vlan H/W offload, the above test check will fail, even if the current code would work just fine (skb->network_header points to the actual IPv4 header). My take is implementing a robust and safe check here would be overkill. Users should attach the action to the correct filter. /P > + goto out; > + > if (!pskb_may_pull(skb, sizeof(*iph) + noff)) > goto drop; >