kernel/linux.git/net/ipv6/ip6_tunnel.c, branch v7.1

ipv6: Implement limits on extension header parsing

2026-05-01T00:21:45+00:00

ipv6_{skip_exthdr,find_hdr}() and ip6_{tnl_parse_tlv_enc_lim, protocol_deliver_rcu}() iterate over IPv6 extension headers until they find a non-extension-header protocol or run out of packet data. The loops have no iteration counter, relying solely on the packet length to bound them. For a crafted packet with 8-byte extension headers filling a 64KB jumbogram, this means a worst case of up to ~8k iterations with a skb_header_pointer call each. ipv6_skip_exthdr(), for example, is used where it parses the inner quoted packet inside an incoming ICMPv6 error: - icmpv6_rcv - checksum validation - case ICMPV6_DEST_UNREACH - icmpv6_notify - pskb_may_pull() <- pull inner IPv6 header - ipv6_skip_exthdr() <- iterates here - pskb_may_pull() - ipprot->err_handler() <- sk lookup The per-iteration cost of ipv6_skip_exthdr itself is generally light, but skb_header_pointer becomes more costly on reassembled packets: the first ~1232 bytes of the inner packet are in the skb's linear area, but the remaining ~63KB are in the frag_list where skb_copy_bits is needed to read data. Initially, the idea was to add a configurable limit via a new sysctl knob with default 8, in line with knobs from commit 47d3d7ac656a ("ipv6: Implement limits on Hop-by-Hop and Destination options"), but two reasons eventually argued against it: - It adds to UAPI that needs to be maintained forever, and upcoming work is restricting extension header ordering anyway, leaving little reason for another sysctl knob - exthdrs_core.c is always built-in even when CONFIG_IPV6=n, where struct net has no .ipv6 member, so the read site would need an ifdef'd fallback to a constant anyway Therefore, just use a constant (IP6_MAX_EXT_HDRS_CNT). All four extension header walking functions are now bound by this limit. Note that the check in ip6_protocol_deliver_rcu() happens right before the goto resubmit, such that we don't have to have a test for ipv6_ext_hdr() in the fast-path. There's an ongoing IETF draft-iurman-6man-eh-occurrences to enforce IPv6 extension headers ordering and occurrence. The latter also discusses security implications. As per RFC8200 section 4.1, the occurrence rules for extension headers provide a practical upper bound which is 8. In order to be conservative, let's define IP6_MAX_EXT_HDRS_CNT as 12 to leave enough room for quirky setups. In the unlikely event that this is still not enough, then we might need to reconsider a sysctl. Signed-off-by: Daniel Borkmann Reviewed-by: Ido Schimmel Reviewed-by: Eric Dumazet Reviewed-by: Justin Iurman Link: https://patch.msgid.link/20260429154648.809751-1-daniel@iogearbox.net Signed-off-by: Jakub Kicinski

ipv6: Cap TLV scan in ip6_tnl_parse_tlv_enc_lim

2026-04-23T18:52:07+00:00

Commit 47d3d7ac656a ("ipv6: Implement limits on Hop-by-Hop and Destination options") added net.ipv6.max_{hbh,dst}_opts_{cnt,len} and applied them in ip6_parse_tlv(), the generic TLV walker invoked from ipv6_destopt_rcv() and ipv6_parse_hopopts(). ip6_tnl_parse_tlv_enc_lim() does not go through ip6_parse_tlv(); it has its own hand-rolled TLV scanner inside its NEXTHDR_DEST branch which looks for IPV6_TLV_TNL_ENCAP_LIMIT. That inner loop is bounded only by optlen, which can be up to 2048 bytes. Stuffing the Destination Options header with 2046 Pad1 (type=0) entries advances the scanner a single byte at a time, yielding ~2000 TLV iterations per extension header. Reusing max_dst_opts_cnt to bound the TLV iterations, matching the semantics from 47d3d7ac656a, would require duplicating ip6_parse_tlv() to also validate Pad1/PadN payload. It would also mandate enforcing max_dst_opts_len, since otherwise an attacker shifts the axis to few options with a giant PadN and recovers the original DoS. Allowing up to 8 options before the tunnel encapsulation limit TLV is liberal enough; in practice encap limit is the first TLV. Thus, go with a hard-coded limit IP6_TUNNEL_MAX_DEST_TLVS (8). Signed-off-by: Daniel Borkmann Reviewed-by: Ido Schimmel Reviewed-by: Justin Iurman Signed-off-by: Jakub Kicinski

ip6_tunnel: use generic for_each_ip_tunnel_rcu macro

2026-04-07T01:41:03+00:00

Remove the locally defined for_each_ip6_tunnel_rcu macro and use the generic for_each_ip_tunnel_rcu from linux/if_tunnel.h instead. This eliminates code duplication and ensures consistency across the kernel tunnel implementations. Signed-off-by: Yue Haibing Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260403084619.4107978-1-yuehaibing@huawei.com Signed-off-by: Jakub Kicinski

ip6_tunnel: clear skb2->cb[] in ip4ip6_err()

2026-03-28T03:24:12+00:00

Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes IPCB(skb2) to __ip_options_echo(), which interprets that cb[] region as struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff at offset 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr value. __ip_options_echo() then reads optlen from attacker-controlled packet data at sptr[rr+1] and copies that many bytes into dopt->__data, a fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE). To fix this we clear skb2->cb[], as suggested by Oskar Kjos. Also add minimal IPv4 header validation (version == 4, ihl >= 5). Fixes: c4d3efafcc93 ("[IPV6] IP6TUNNEL: Add support to IPv4 over IPv6 tunnel.") Reported-by: Oskar Kjos Signed-off-by: Eric Dumazet Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260326155138.2429480-1-edumazet@google.com Signed-off-by: Jakub Kicinski

ipv6: use dst6_mtu() instead of dst_mtu()

2026-02-03T01:49:29+00:00

When we expect an IPv6 dst, use dst6_mtu() instead of dst_mtu() to save some code space. Due to current dst6_mtu() implementation, only convert users in IPv6 stack. Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260130210303.3888261-7-edumazet@google.com Signed-off-by: Jakub Kicinski

ipv6: pass proto by value to ipv6_push_nfrag_opts() and ipv6_push_frag_opts()

2026-02-03T01:49:28+00:00

With CONFIG_STACKPROTECTOR_STRONG=y, it is better to avoid passing a pointer to an automatic variable. Change these exported functions to return 'u8 proto' instead of void. - ipv6_push_nfrag_opts() - ipv6_push_frag_opts() For instance, replace ipv6_push_frag_opts(skb, opt, &proto); with: proto = ipv6_push_frag_opts(skb, opt, proto); Note that even after this change, ip6_xmit() has to use a stack canary because of @first_hop variable. Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260130210303.3888261-2-edumazet@google.com Signed-off-by: Jakub Kicinski

netfilter: flowtable: Add IP6IP6 rx sw acceleration

2026-01-29T08:52:06+00:00

Introduce sw acceleration for rx path of IP6IP6 tunnels relying on the netfilter flowtable infrastructure. Subsequent patches will add sw acceleration for IP6IP6 tunnels tx path. IP6IP6 rx sw acceleration can be tested running the following scenario where the traffic is forwarded between two NICs (eth0 and eth1) and an IP6IP6 tunnel is used to access a remote site (using eth1 as the underlay device): ETH0 -- TUN0 <==> ETH1 -- [IP network] -- TUN1 (2001:db8:3::2) $ip addr show 6: eth0: mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 00:00:22:33:11:55 brd ff:ff:ff:ff:ff:ff inet6 2001:db8:1::2/64 scope global nodad valid_lft forever preferred_lft forever 7: eth1: mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 00:11:22:33:11:55 brd ff:ff:ff:ff:ff:ff inet6 2001:db8:2::1/64 scope global nodad valid_lft forever preferred_lft forever 8: tun0@NONE: mtu 1480 qdisc noqueue state UNKNOWN group default qlen 1000 link/tunnel6 2001:db8:2::1 peer 2001:db8:2::2 permaddr ce9c:2940:7dcc:: inet6 2002:db8:1::1/64 scope global nodad valid_lft forever preferred_lft forever $ip -6 route show 2001:db8:1::/64 dev eth0 proto kernel metric 256 pref medium 2001:db8:2::/64 dev eth1 proto kernel metric 256 pref medium 2002:db8:1::/64 dev tun0 proto kernel metric 256 pref medium default via 2002:db8:1::2 dev tun0 metric 1024 pref medium $nft list ruleset table inet filter { flowtable ft { hook ingress priority filter devices = { eth0, eth1 } } chain forward { type filter hook forward priority filter; policy accept; meta l4proto { tcp, udp } flow add @ft } } Reproducing the scenario described above using veths I got the following results: - TCP stream received from the IPIP tunnel: - net-next: (baseline) ~ 81Gbps - net-next + IP6IP6 flowtbale support: ~112Gbps Signed-off-by: Lorenzo Bianconi Signed-off-by: Florian Westphal

ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()

2026-01-10T02:14:08+00:00

Blamed commit did not take care of VLAN encapsulations as spotted by syzbot [1]. Use skb_vlan_inet_prepare() instead of pskb_inet_may_pull(). [1] BUG: KMSAN: uninit-value in __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline] BUG: KMSAN: uninit-value in INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline] BUG: KMSAN: uninit-value in IP6_ECN_decapsulate+0x7a8/0x1fa0 include/net/inet_ecn.h:321 __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline] INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline] IP6_ECN_decapsulate+0x7a8/0x1fa0 include/net/inet_ecn.h:321 ip6ip6_dscp_ecn_decapsulate+0x16f/0x1b0 net/ipv6/ip6_tunnel.c:729 __ip6_tnl_rcv+0xed9/0x1b50 net/ipv6/ip6_tunnel.c:860 ip6_tnl_rcv+0xc3/0x100 net/ipv6/ip6_tunnel.c:903 gre_rcv+0x1529/0x1b90 net/ipv6/ip6_gre.c:-1 ip6_protocol_deliver_rcu+0x1c89/0x2c60 net/ipv6/ip6_input.c:438 ip6_input_finish+0x1f4/0x4a0 net/ipv6/ip6_input.c:489 NF_HOOK include/linux/netfilter.h:318 [inline] ip6_input+0x9c/0x330 net/ipv6/ip6_input.c:500 ip6_mc_input+0x7ca/0xc10 net/ipv6/ip6_input.c:590 dst_input include/net/dst.h:474 [inline] ip6_rcv_finish+0x958/0x990 net/ipv6/ip6_input.c:79 NF_HOOK include/linux/netfilter.h:318 [inline] ipv6_rcv+0xf1/0x3c0 net/ipv6/ip6_input.c:311 __netif_receive_skb_one_core net/core/dev.c:6139 [inline] __netif_receive_skb+0x1df/0xac0 net/core/dev.c:6252 netif_receive_skb_internal net/core/dev.c:6338 [inline] netif_receive_skb+0x57/0x630 net/core/dev.c:6397 tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485 tun_get_user+0x5c0e/0x6c60 drivers/net/tun.c:1953 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0xbe2/0x15d0 fs/read_write.c:686 ksys_write fs/read_write.c:738 [inline] __do_sys_write fs/read_write.c:749 [inline] __se_sys_write fs/read_write.c:746 [inline] __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746 x64_sys_call+0x30ab/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xd3/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f Uninit was created at: slab_post_alloc_hook mm/slub.c:4960 [inline] slab_alloc_node mm/slub.c:5263 [inline] kmem_cache_alloc_node_noprof+0x9e7/0x17a0 mm/slub.c:5315 kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:586 __alloc_skb+0x805/0x1040 net/core/skbuff.c:690 alloc_skb include/linux/skbuff.h:1383 [inline] alloc_skb_with_frags+0xc5/0xa60 net/core/skbuff.c:6712 sock_alloc_send_pskb+0xacc/0xc60 net/core/sock.c:2995 tun_alloc_skb drivers/net/tun.c:1461 [inline] tun_get_user+0x1142/0x6c60 drivers/net/tun.c:1794 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0xbe2/0x15d0 fs/read_write.c:686 ksys_write fs/read_write.c:738 [inline] __do_sys_write fs/read_write.c:749 [inline] __se_sys_write fs/read_write.c:746 [inline] __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746 x64_sys_call+0x30ab/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xd3/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f CPU: 0 UID: 0 PID: 6465 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 Fixes: 8d975c15c0cd ("ip6_tunnel: make sure to pull inner header in __ip6_tnl_rcv()") Reported-by: syzbot+d4dda070f833dc5dc89a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/695e88b2.050a0220.1c677c.036d.GAE@google.com/T/#u Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260107163109.4188620-1-edumazet@google.com Signed-off-by: Jakub Kicinski

net/ip6_tunnel: Prevent perpetual tunnel growth

2025-10-14T00:43:46+00:00

Similarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too. While ipv4 tunnel headroom adjustment growth was limited in commit 5ae1e9922bbd ("net: ip_tunnel: prevent perpetual headroom growth"), ipv6 tunnel yet increases the headroom without any ceiling. Reflect ipv4 tunnel headroom adjustment limit on ipv6 version. Credits to Francesco Ruggeri, who was originally debugging this issue and wrote local Arista-specific patch and a reproducer. Fixes: 8eb30be0352d ("ipv6: Create ip6_tnl_xmit") Cc: Florian Westphal Cc: Francesco Ruggeri Signed-off-by: Dmitry Safonov Link: https://patch.msgid.link/20251009-ip6_tunnel-headroom-v2-1-8e4dbd8f7e35@arista.com Signed-off-by: Jakub Kicinski

ipv6: adopt skb_dst_dev() and skb_dst_dev_net[_rcu]() helpers

2025-07-02T21:32:30+00:00

Use the new helpers as a step to deal with potential dst->dev races. v2: fix typo in ipv6_rthdr_rcv() (kernel test robot ) Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250630121934.3399505-10-edumazet@google.com Signed-off-by: Jakub Kicinski