net/sched: act_ife: ensure ETH_HLEN is pullable after decap
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PATCH 1/1 net/sched: act_ife: ensure ETH_HLEN is pullable after decap
From: Yong Wang <[email protected]>
tcf_ife_decode() calls eth_type_trans() after ife_decode() removes the outer IFE header and metadata. However, ife_decode() only makes the outer IFE header area pullable before advancing skb->data.
As a result, the decapsulated inner Ethernet header may still be shorter than ETH_HLEN in the linear data area, or entirely reside in frags. eth_type_trans() then operates on an skb that does not satisfy its expected Ethernet header access requirements, which can trigger a BUG in the pull path.
Fix this by requiring ETH_HLEN to be pullable before calling eth_type_trans(). If that fails, drop the packet just like the other decode error paths in tcf_ife_decode().
--- net/sched/act_ife.c | 5 +++++ 1 file changed, 5 insertions(+)
net/sched/act_ife.c +5 -0
@@ -759,6 +759,11 @@ static int tcf_ife_decode(struct sk_buff *skb, const struct tc_action *a,return TC_ACT_SHOT ; } +if (!pskb_may_pull (skb,ETH_HLEN )) { +qstats_drop_inc (this_cpu_ptr (ife->common.cpu_qstats)); +return TC_ACT_SHOT ; + } + skb->protocol =eth_type_trans (skb, skb->dev);skb_reset_network_header (skb);
Signature · 1 line
2.34.1
Jamal Hadi Salim
maintainerQuoted 7 lines · Ren Wei
From: Yong Wang <[email protected]>
tcf_ife_decode()callseth_type_trans()afterife_decode()removes the outer IFE header and metadata. However,ife_decode()only makes the outer IFE header area pullable before advancingskb->data.
Quoted 6 lines
As a result, the decapsulated inner Ethernet header may still be shorter than
ETH_HLENin the linear data area, or entirely reside in frags.eth_type_trans()then operates on an skb that does not satisfy its expected Ethernet header access requirements, which can trigger a BUG in the pull path.
From inspection this looks legit. I did not run your poc. Could you create a tdc test instead? You should be able to craft a scapy ethernet frame using nsplugin. Something like this:
Ether(type=0xED3E) / Raw(b'\\x00\\x02\\xaa') would suffice. That would be more helpful for future reference as well.
Quoted 20 lines
Fix this by requiring
ETH_HLENto be pullable before callingeth_type_trans(). If that fails, drop the packet just like the other decode error paths intcf_ife_decode().Fixes ef6980b6becb ("introduce IFE action")Reported-by Yuan Tan <[email protected]>Reported-by Xin Liu <[email protected]>Assisted-by Codex:gpt-5.4Signed-off-by Yong Wang <[email protected]>Signed-off-by Ren Wei <[email protected]>--- net/sched/act_ife.c | 5 +++++ 1 file changed, 5 insertions(+)net/sched/act_ife.c +0
-0
net/sched/act_ife.c static int tcf_ife_decode(struct sk_buff *skb, const struct tc_action *a, · line 768
Quoted 10 lines
net/sched/act_ife.c +5
-0@@ -759,6 +759,11 @@ static int tcf_ife_decode(struct sk_buff *skb, const struct tc_action *a,return TC_ACT_SHOT ; } +if (!pskb_may_pull (skb,ETH_HLEN )) { +qstats_drop_inc (this_cpu_ptr (ife->common.cpu_qstats)); +return TC_ACT_SHOT ; + } + skb->protocol =eth_type_trans (skb, skb->dev);skb_reset_network_header (skb);
We already do a pull in ife_decode(), so why not just extend that to have ETH_HLEN?
Given that IFE is always encaped over ethernet frames it should be fine to assume ethernet header.
i.e something like:
- if (unlikely(!pskb_may_pull(skb, total_pull)))
+ if (unlikely(!pskb_may_pull(skb, total_pull + ETH_HLEN)))
cheers,
jamal
Quoted 4 lines
net/sched/act_ife.c +0
-1--2.34.1
Quoted 15 lines · Jamal Hadi Salim
Quoted 7 lines · Ren Wei
From: Yong Wang <[email protected]>
tcf_ife_decode()callseth_type_trans()afterife_decode()removes the outer IFE header and metadata. However,ife_decode()only makes the outer IFE header area pullable before advancingskb->data.Quoted 6 lines
As a result, the decapsulated inner Ethernet header may still be shorter than
ETH_HLENin the linear data area, or entirely reside in frags.eth_type_trans()then operates on an skb that does not satisfy its expected Ethernet header access requirements, which can trigger a BUG in the pull path.
Quoted 6 lines
[...]
From inspection this looks legit. I did not run your poc. Could you create a tdc test instead? You should be able to craft a scapy ethernet frame using nsplugin. Something like this:
Ether(type=0xED3E) / Raw(b'\\x00\\x02\\xaa') would suffice. That would be more helpful for future reference as well.
Can you try to run this tdc test?
cheers,
Victor
From 6b7ba3d553dfa8e76bdad8438f9585fda2b2fc35 Mon Sep 17 00:00:00 2001
From: Victor Nogueira <[email protected]>
Date: Mon, 8 Jun 2026 10:03:48 -0300
Subject: [PATCH net] selftests/tc-testing: Verify IFE can handle truncated
inner Ethernet header
Add a tdc test that exercises the act_ife decode path with a malformed IFE packet whose encapsulated inner Ethernet header is truncated.
The injected frame has a valid outer Ethernet header (ethertype 0xED3E) and a minimal IFE header (metalen 2, i.e. no metadata TLVs), but the payload that should hold the original frame is a single byte instead of a full Ethernet header. Once ife_decode() strips the outer header and the IFE metadata, fewer than ETH_HLEN bytes are left, which previously let eth_type_trans() read past the end of the linear data.
--- .../tc-testing/tc-tests/actions/ife.json | 55 +++++++++++++++++++ 1 file changed, 55 insertions(+)
tools/testing/selftests/tc-testing/tc-tests/actions/ife.json +55 -0
@@ -1378,5 +1378,60 @@ "teardown": [ "$TC actions flush action ife" ] + }, + { + "id": "4e6b", + "name": "Decode IFE packet with truncated inner Ethernet header", + "category": [ + "actions", + "ife" + ], + "plugins": { + "requires": [ + "nsPlugin", + "scapyPlugin" + ] + }, + "setup": [ + [ + "$TC actions flush action ife", + 0, + 1, + 255 + ], + "$TC qdisc add dev $DEV1 clsact" + ], + "scapy": [ + { + "iface": "$DEV0", + "count": 1, + "packet": "Ether(type=0xED3E) / Raw(b'\\x00\\x02\\xaa')" + } + ], + "cmdUnderTest": "$TC filter add dev $DEV1 ingress protocol all matchall action ife decode pipe index 10", + "expExitCode": "0", + "verifyCmd": "$TC -s -j actions get action ife index 10", + "matchJSON": [ + { + "total acts": 0 + }, + { + "actions": [ + { + "kind": "ife", + "mode": "decode", + "index": 10, + "stats": { + "bytes": 3, + "packets": 1, + "drops": 1 + } + } + ] + } + ], + "teardown": [ + "$TC qdisc del dev $DEV1 clsact" + ] } ]
Signature · 1 line
2.54.0