[PATCH net v3 1/2] net/sched: act_pedit: require matching IPv4 L4 protocol

[PATCH net v3 1/2] net/sched: act_pedit: require matching IPv4 L4 protocol

[Samuel Moelius]

The extended IPv4 L4 header mode in act_pedit can select TCP or UDP
header fields without confirming that the IPv4 protocol field matches
the selected transport header.

That lets a rule written for TCP or UDP modify unrelated payload bytes
in a packet carrying a different protocol.

Verify that the IPv4 header is long enough, that the protocol matches
the selected TCP or UDP header, and that the packet is not a non-initial
fragment before applying TCP or UDP extended header edits.

Fixes: 6c02568fd1ae ("net/sched: act_pedit: Parse L3 Header for L4 offset")
Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
---
Changes in v2:
  - Add check of iph->frag_off & htons(IP_OFFSET)
 net/sched/act_pedit.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
index bd3b1da3cd63..0d652dea4a69 100644
--- a/net/sched/act_pedit.c
+++ b/net/sched/act_pedit.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/overflow.h>
 #include <linux/unaligned.h>
+#include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
@@ -331,6 +332,9 @@ static int pedit_l4_skb_offset(struct sk_buff *skb, int *hoffset, const int head
 
 		if (!iph)
 			goto out;
+		if (iph->ihl < 5 || iph->protocol != header_type ||
+		    (iph->frag_off & htons(IP_OFFSET)))
+			goto out;
 		*hoffset = noff + iph->ihl * 4;
 		ret = 0;
 		break;
-- 
2.43.0

[PATCH net v3 2/2] net/sched: act_pedit: require matching IPv4 L4 protocol

[Samuel Moelius]

From: Victor Nogueira <victor@mojatatu.com>

Add a tdc test that checks the act_pedit extended L4 header mode does not
edit a packet whose IPv4 protocol does not match the selected transport
header.

The test installs an ingress pedit rule that sets the UDP destination
port, then injects a TCP packet with dport 2222. The UDP and TCP
destination ports sit at the same L4 offset, so a buggy kernel rewrites
the TCP dport. A second flower filter matches TCP dport 2222 and drops
the packet through an indexed gact action; the test then verifies via
JSON that this action saw exactly one packet, i.e. the dport was left
untouched and still matched 2222.

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
---
Changes in v3:
  - Add test

 .../tc-testing/tc-tests/actions/pedit.json    | 49 +++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/actions/pedit.json b/tools/testing/selftests/tc-testing/tc-tests/actions/pedit.json
index 37c4103321749..d8b685cfc62de 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/actions/pedit.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/actions/pedit.json
@@ -1920,5 +1920,54 @@
         "teardown": [
             "$TC actions flush action pedit"
         ]
+    },
+    {
+        "id": "1a4f",
+        "name": "Pedit udp dport should not mangle TCP packet dport",
+        "category": [
+            "actions",
+            "pedit"
+        ],
+        "plugins": {
+            "requires": [
+                "nsPlugin",
+                "scapyPlugin"
+            ]
+        },
+        "setup": [
+            "$TC qdisc add dev $DEV1 clsact",
+            "$TC filter add dev $DEV1 ingress protocol ip pref 1 matchall action pedit ex munge udp dport set 18053 continue"
+        ],
+        "cmdUnderTest": "$TC filter add dev $DEV1 ingress protocol ip pref 2 flower ip_proto tcp dst_port 2222 action drop index 1",
+        "scapy": {
+            "iface": "$DEV0",
+            "count": 1,
+            "packet": "Ether()/IP(dst='10.10.10.1')/TCP(dport=2222)"
+        },
+        "expExitCode": "0",
+        "verifyCmd": "$TC -j -s actions get action gact index 1",
+        "matchJSON": [
+            {
+                "total acts": 0
+            },
+            {
+                "actions": [
+                    {
+                        "order": 1,
+                        "kind": "gact",
+                        "control_action": {
+                            "type": "drop"
+                        },
+                        "index": 1,
+                        "stats": {
+                            "packets": 1
+                        }
+                    }
+                ]
+            }
+        ],
+        "teardown": [
+            "$TC qdisc del dev $DEV1 clsact"
+        ]
     }
 ]
-- 
2.54.0