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Date: Fri, 31 Jul 2026 17:50:22 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Ren Wei <enjou1224z@gmail.com>
Cc: netdev@vger.kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net,
 edumazet@google.com, pabeni@redhat.com, vega@nebusec.ai,
 bronzed_45_vested@icloud.com
Subject: Re: [PATCH net v3] net: loopback: ensure Ethernet header is linear
 before eth_type_trans
Message-ID: <20260731175022.18fd8744@kernel.org>
In-Reply-To: <2d4e79d252a57bdad83435999dddf2c4b708dcfa.1785049236.git.bronzed_45_vested@icloud.com>
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On Tue, 28 Jul 2026 23:04:14 +0800 Ren Wei wrote:
> loopback_xmit() passes skbs to eth_type_trans(), which expects a
> complete Ethernet header in linear data before consuming ETH_HLEN
> bytes.
> 
> If an earlier path stripped or shortened the Ethernet header, a
> non-linear skb can reach loopback with skb->len >= ETH_HLEN but fewer
> than ETH_HLEN bytes in the linear area. eth_type_trans() then triggers
> a BUG in __skb_pull(), causing a short-packet handling crash.
> 
> Check pskb_may_pull(skb, ETH_HLEN) before calling
> eth_type_trans(). This also rejects packets whose total length is
> shorter than ETH_HLEN. Account rejected packets as tx drops instead of
> crashing.
> 
> The analogous VRF path is already protected because its IPv4 and IPv6
> callers pull the Ethernet and network headers before calling
> vrf_local_xmit().

How are we getting the short frame in the xmit path?
Please repost with the repro like you do for other bugs...