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[209.147.138.4]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33bf5af4f0bsm4138749eec.24.2026.09.15.21.11.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 21:11:03 -0700 (PDT) From: Xiang Mei To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org, co+ff13a35f73bb7891@bugs.sh, stable@vger.kernel.org, Xiang Mei Subject: [PATCH net] bpf: lwt: clear stale IP control block after pushing an encap header Date: Tue, 15 Sep 2026 21:11:02 -0700 Message-ID: <20260916041102.1914333-1-xmei5@asu.edu> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" bpf_lwt_push_ip_encap() prepends an encapsulation header and calls skb_reset_network_header(), but leaves the IP control block describing the inner header. Its offsets are relative to the network header, so they now point into the encapsulated packet. On an ingress lwt-bpf encap route a forwarded packet carrying a Record Route option then reaches __ip_options_echo() with a stale opt->rr. It takes the option length from the packet and copies up to 255 bytes into the fixed-size option storage on the __icmp_send() stack. ip_forward_options() writes at a packet-controlled offset for the same reason. Clear the stale state once the outer header is in place, as the tunnel encapsulators do and as seg6_local.c was taught to do in commit f967455fb2a5 ("seg6: reset IP6CB after IPv6 decapsulation") and commit 44930446dde4 ("ipv6: seg6: clear IPv4 control block on IPIP decapsulation"). BUG: KASAN: stack-out-of-bounds in __ip_options_echo (net/ipv4/ip_options= .c:96) Write of size 255 at addr ffff8880bee08930 by task exploit/150 Call Trace: __asan_memcpy (mm/kasan/shadow.c:106) __ip_options_echo (net/ipv4/ip_options.c:96) __icmp_send (net/ipv4/icmp.c:949) ip_forward (./include/net/icmp.h:43 net/ipv4/ip_forward.c:176) lwtunnel_input (net/core/lwtunnel.c:465) ip_rcv (net/ipv4/ip_input.c:612) __netif_receive_skb_one_core (net/core/dev.c:6264) process_backlog (net/core/dev.c:6728) __napi_poll (net/core/dev.c:7787) net_rx_action (net/core/dev.c:8007) handle_softirqs (kernel/softirq.c:645) do_softirq.part.0 (kernel/softirq.c:546) __local_bh_enable_ip (kernel/softirq.c:473) __dev_queue_xmit (net/core/dev.c:4961) packet_sendmsg (net/packet/af_packet.c:3143) __sys_sendto (net/socket.c:2281) __x64_sys_sendto (net/socket.c:2288) do_syscall_64 (arch/x86/entry/syscall_64.c:84) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Cc: stable@vger.kernel.org Fixes: 52f278774e79 ("bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_= encap") Reported-by: Assisted-by: LLM Signed-off-by: Xiang Mei --- net/core/lwt_bpf.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c index da49364ec63d..17be476b5717 100644 --- a/net/core/lwt_bpf.c +++ b/net/core/lwt_bpf.c @@ -649,6 +649,18 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *h= dr, u32 len, bool ingress) if (ingress) skb_postpush_rcsum(skb, iph, len); skb_reset_network_header(skb); + if (ipv4) { + memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt)); + } else { + bool l3slave =3D ipv6_l3mdev_skb(IP6CB(skb)->flags); + int iif =3D IP6CB(skb)->iif; + + memset(IP6CB(skb), 0, sizeof(*IP6CB(skb))); + IP6CB(skb)->iif =3D iif; + IP6CB(skb)->nhoff =3D offsetof(struct ipv6hdr, nexthdr); + if (l3slave) + IP6CB(skb)->flags |=3D IP6SKB_L3SLAVE; + } if (is_udp_tunnel) { size_t iph_sz =3D ipv4 ? iph->ihl * 4 : sizeof(struct ipv6hdr); =20 --=20 2.43.0