net/sched: act_ife: Only operate on Ethernet frames

act_ife encapsulates/decapsulates the original Ethernet header and uses
skb->dev->hard_header_len as the length of that header. That is only
correct for Ethernet devices: on a device where hard_header_len does not
match the L2 header that was actually pulled (PPP reports PPP_HDRLEN
while nothing is stripped on ingress), the ingress skb_push()/skb_pull()
use the wrong length and can hit skb_under_panic when headroom is tight.

IFE is Ethernet-only by design - it builds an outer ethhdr, rewrites
h_source/h_dest/h_proto, and calls eth_type_trans() on decode - so
instead of trying to make the offsets work for arbitrary link types,
simply drop packets that do not carry an Ethernet header.

Checking skb->dev->type alone is not enough. We have to cater for a
corner case where mirred can redirect an skb from a non-Ethernet device
to an Ethernet one, and skb->dev then says nothing about the framing the
skb actually has: an skb redirected from ppp0 reaches the target's ingress
hook with mac_len 0 and no Ethernet header at all. So at ingress also
require mac_len to be ETH_HLEN. On egress mac_len is not maintained, so
the device type is all we have; a bogus redirect there yields a malformed
frame rather than an out-of-bounds push, and it would be malformed with or
without IFE.

That corner case is not theoretical - redirecting from ppp0 into a veth
that has an ife encode action on its ingress hook panics without this
patch:

  skbuff: skb_under_panic: len:98 put:14 head:ffff88800e410000
          data:ffff88800e40fff5 tail:0x57 end:0x640 dev:veth3
  kernel BUG at net/core/skbuff.c:214!
  Call Trace:
   skb_push (net/core/skbuff.c:224 net/core/skbuff.c:2657)
   tcf_ife_act (net/sched/act_ife.c:829 net/sched/act_ife.c:874)
   tc_run (net/core/dev.c:4463)
   netif_receive_skb (net/core/dev.c:6463 net/core/dev.c:6522)
   tcf_mirred_to_dev (net/sched/act_mirred.c:248 net/sched/act_mirred.c:328)
   tcf_mirred_act (net/sched/act_mirred.c:489)
   tc_run (net/core/dev.c:4463)
   process_backlog (net/core/dev.c:6728)

With Ethernet framing guaranteed, use ETH_HLEN instead of
hard_header_len.

Fixes: 295a6e06d21e ("net/sched: act_ife: Change to use ife module")
Reported-by: vega@nebusec.ai
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20260821164031.32824-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 7 insertions, 7 deletions

diff --git a/net/ife/ife.c b/net/ife/ife.c
index 7a75947a31e3..2ddf725d3389 100644
--- a/net/ife/ife.c
+++ b/net/ife/ife.c
@@ -37,7 +37,7 @@ void *ife_encode(struct sk_buff *skb, u16 metalen)
 	 * where ORIGDATA = original ethernet header ...
 	 */
 	int hdrm = metalen + IFE_METAHDRLEN;
-	int total_push = hdrm + skb->dev->hard_header_len;
+	int total_push = hdrm + ETH_HLEN;
 	struct ifeheadr *ifehdr;
 	struct ethhdr *iethh;	/* inner ether header */
 	int skboff = 0;
@@ -50,9 +50,9 @@ void *ife_encode(struct sk_buff *skb, u16 metalen)
 	iethh = (struct ethhdr *) skb->data;
 
 	__skb_push(skb, total_push);
-	memcpy(skb->data, iethh, skb->dev->hard_header_len);
+	memcpy(skb->data, iethh, ETH_HLEN);
 	skb_reset_mac_header(skb);
-	skboff += skb->dev->hard_header_len;
+	skboff += ETH_HLEN;
 
 	/* total metadata length */
 	ifehdr = (struct ifeheadr *) (skb->data + skboff);
@@ -69,12 +69,12 @@ void *ife_decode(struct sk_buff *skb, u16 *metalen)
 	int total_pull;
 	u16 ifehdrln;
 
-	if (!pskb_may_pull(skb, skb->dev->hard_header_len + IFE_METAHDRLEN))
+	if (!pskb_may_pull(skb, ETH_HLEN + IFE_METAHDRLEN))
 		return NULL;
 
-	ifehdr = (struct ifeheadr *) (skb->data + skb->dev->hard_header_len);
+	ifehdr = (struct ifeheadr *)(skb->data + ETH_HLEN);
 	ifehdrln = ntohs(ifehdr->metalen);
-	total_pull = skb->dev->hard_header_len + ifehdrln;
+	total_pull = ETH_HLEN + ifehdrln;
 
 	if (unlikely(ifehdrln < 2))
 		return NULL;
@@ -82,7 +82,7 @@ void *ife_decode(struct sk_buff *skb, u16 *metalen)
 	if (unlikely(!pskb_may_pull(skb, total_pull + ETH_HLEN)))
 		return NULL;
 
-	ifehdr = (struct ifeheadr *)(skb->data + skb->dev->hard_header_len);
+	ifehdr = (struct ifeheadr *)(skb->data + ETH_HLEN);
 	skb_set_mac_header(skb, total_pull);
 	__skb_pull(skb, total_pull);
 	*metalen = ifehdrln - IFE_METAHDRLEN;