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Thu, 17 Sep 2026 00:22:46 -0700 (PDT) Received: from localhost.localdomain ([139.159.170.86]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-87200d4cb44sm2463091b3a.13.2026.09.17.00.22.41 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 17 Sep 2026 00:22:46 -0700 (PDT) From: Qihang To: netdev@vger.kernel.org Cc: steffen.klassert@secunet.com, herbert@gondor.apana.org.au, Qihang , stable@vger.kernel.org Subject: [PATCH] xfrm: validate ihl in xfrm4_transport_output() Date: Thu, 17 Sep 2026 15:22:26 +0800 Message-ID: <20260917072226.80788-1-q.h.hack.winter@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit xfrm4_transport_output() reads the IPv4 header length (ihl) from the packet and uses it for __skb_pull() and memmove() without checking it against skb->len, so a frame with ihl * 4 > skb->len underflows skb->len to a huge value. Packets injected into an xfrm interface (e.g. AF_PACKET on an xfrmi device) reach xfrm output without the pskb_may_pull(ihl * 4) check that ip_rcv_core() applies to received traffic. The underflowed length then flows into esp_output() and the crypto scatterlist setup, where every length in the underflow window ends in a fatal fault (BUG_ON in __skb_to_sgvec(), or a wild scatterlist access in the crypto layer). This is a deterministic local denial of service reachable by an unprivileged user through a user and network namespace. xfrm6_transport_output() bounds the header length via xfrm6_hdr_offset() and the IPv4 tunnel/BEET paths use the constant XFRM_MODE_SKB_CB(skb)->ihl; only IPv4 transport uses the live, unvalidated value. Reject the packet when ihl exceeds skb->len. Fixes: b59f45d0b2878 ("[IPSEC] xfrm: Abstract out encapsulation modes") Cc: stable@vger.kernel.org Signed-off-by: Qihang --- net/xfrm/xfrm_output.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c --- a/net/xfrm/xfrm_output.c +++ b/net/xfrm/xfrm_output.c @@ -66,6 +66,9 @@ static int xfrm4_transport_output(struct xfrm_state *x, struct sk_buff *skb) struct iphdr *iph = ip_hdr(skb); int ihl = iph->ihl * 4; + if (ihl > skb->len) + return -EINVAL; + if (!skb->inner_protocol) skb_set_inner_transport_header(skb, skb_transport_offset(skb)); -- 2.46.0