llc: reserve device headroom for allocated frames

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llc_alloc_frame() reserves link-layer headroom using the device type.
This is insufficient for stacked Ethernet devices such as VLAN devices,
where vlan_dev_hard_header() pushes a VLAN header before the lower
device's Ethernet header. An LLC response on such a device can
therefore underflow skb headroom in eth_header().

Use LL_RESERVED_SPACE() to account for the device's actual required
headroom while preserving the existing LLC device-type check.

Fixes: bf9ae5386b ("llc: use dev_hard_header")
Cc: stable@vger.kernel.org
Reported-by: VEGA <vega@nebusec.ai>
Signed-off-by: Zixuan Chai <petalzu987@gmail.com>
Signed-off-by: Ren Wei <weir@nebusec.ai>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260924012613.2533934-1-weir@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Zixuan Chai 2026-09-24 09:26:05 +08:00 • committed by Jakub Kicinski

parent 488089055b

commit 72b5b9a28b

1 changed files with 4 additions and 4 deletions

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net/llc/llc_sap.c

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