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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] xfrm: fix missing headroom check in xfrm_dev_direct_output Date: Mon, 18 May 2026 10:04:09 +0200 Message-Id: <20260518080410.11119-1-gunther.muller2008@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260517111940.8987-1-gunther.muller2008@gmail.com> References: <20260517111940.8987-1-gunther.muller2008@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Ensure the skb has enough headroom for the hardware offload device's hard_header_len. If the headroom is insufficient (e.g., when routing through certain virtual or tunnel devices), __skb_push() underflows skb->data below skb->head, causing silent memory corruption. Fix this by using skb_cow_head() to dynamically expand headroom if needed, and switch to the checked skb_push() variant. Fixes: 5eddd76ec2fd ("xfrm: fix tunnel mode TX datapath in packet offload m= ode") Signed-off-by: G=C3=BCnther Muller --- net/xfrm/xfrm_output.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c index cc35c2fcbb..35f974d209 100644 --- a/net/xfrm/xfrm_output.c +++ b/net/xfrm/xfrm_output.c @@ -649,7 +649,10 @@ static int xfrm_dev_direct_output(struct sock *sk, str= uct xfrm_state *x, * to netdevice. */ skb->dev =3D x->xso.dev; - __skb_push(skb, skb->dev->hard_header_len); + err =3D skb_cow_head(skb, skb->dev->hard_header_len); + if (err) + return err; + skb_push(skb, skb->dev->hard_header_len); return dev_queue_xmit(skb); } =20 --=20 2.39.5