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kernel: generic: patch: 802.2+LLC - set transport_header offset

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Conversion to DSA broke 802.2+LLC+SNAP packet processing. Frames
received by napi_complete_done with GRO and DSA have transport_header
set two bytes short, or pointing 2 bytes before network_header &
skb->data. As snap_rcv expects transport_header to point to SNAP
header (OID:PID) after LLC processing advances offset over LLC header
(llc_rcv & llc_fixup_skb), code doesn't find a match and packet is
dropped.

Image built at this commit operates properly:
  86dadeba48 - generic: add patch for GPON-ONU-34-20BI quirk
Image built at following commit exhibits the issue:
  337e36e0ef - ipq806x: convert each device to DSA implementation

As issue is LLC specific, to avoid impacting non-LLC traffic, and to
follow up on original assumption made on kernel commit fda55eca5a33
("net: introduce skb_transport_header_was_set()") stating "network
stacks usually reset the transport header anyway", llc_fixup_skb to
reset and advance the offset. llc_fixup_skb already assumes the LLC
header is at skb->data, and by definition SNAP header immediately
follows.

Signed-off-by: Antonio Pastor <antonio.pastor@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17220
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit da7ab64f1f)
This commit is contained in:
Antonio Pastor 2024-12-20 11:28:45 -05:00 committed by Robert Marko
parent 5b4a081f47
commit 76a546a83a
1 changed files with 52 additions and 0 deletions
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52
target/linux/generic/backport-6.6/902-net-llc-reset-skb-transport_header.patch Normal file
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@ -0,0 +1,52 @@
From a024e377efed31ecfb39210bed562932321345b3 Mon Sep 17 00:00:00 2001
From: Antonio Pastor <antonio.pastor@gmail.com>
Date: Tue, 24 Dec 2024 20:07:20 -0500
Subject: [PATCH] net: llc: reset skb->transport_header
802.2+LLC+SNAP frames received by napi_complete_done with GRO and DSA
have skb->transport_header set two bytes short, or pointing 2 bytes
before network_header & skb->data. As snap_rcv expects transport_header
to point to SNAP header (OID:PID) after LLC processing advances offset
over LLC header (llc_rcv & llc_fixup_skb), code doesn't find a match
and packet is dropped.
Between napi_complete_done and snap_rcv, transport_header is not used
until __netif_receive_skb_core, where originally it was being reset.
Commit fda55eca5a33 ("net: introduce skb_transport_header_was_set()")
only does so if not set, on the assumption the value was set correctly
by GRO (and also on assumption that "network stacks usually reset the
transport header anyway"). Afterwards it is moved forward by
llc_fixup_skb.
Locally generated traffic shows up at __netif_receive_skb_core with no
transport_header set and is processed without issue. On a setup with
GRO but no DSA, transport_header and network_header are both set to
point to skb->data which is also correct.
As issue is LLC specific, to avoid impacting non-LLC traffic, and to
follow up on original assumption made on previous code change,
llc_fixup_skb to reset the offset after skb pull. llc_fixup_skb
assumes the LLC header is at skb->data, and by definition SNAP header
immediately follows.
Fixes: fda55eca5a33 ("net: introduce skb_transport_header_was_set()")
Signed-off-by: Antonio Pastor <antonio.pastor@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241225010723.2830290-1-antonio.pastor@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
net/llc/llc_input.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/llc/llc_input.c
+++ b/net/llc/llc_input.c
@@ -124,8 +124,8 @@ static inline int llc_fixup_skb(struct s
if (unlikely(!pskb_may_pull(skb, llc_len)))
return 0;
- skb->transport_header += llc_len;
skb_pull(skb, llc_len);
+ skb_reset_transport_header(skb);
if (skb->protocol == htons(ETH_P_802_2)) {
__be16 pdulen;
s32 data_size;