KASAN: slab-out-of-bounds Read in __xfrm_decode_session

Status: upstream: reported C repro on 2026/03/22 10:21
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+3df7d934c08936248f4d@syzkaller.appspotmail.com
First crash: 134d, last: 134d
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/03/23 linux-6.6.y (ToT) 4fc00fe35d46 C [report] KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/03/23 upstream (ToT) c369299895a5 C Didn't crash
▶ ▼ Similar bugs (13)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 KASAN: slab-use-after-free Read in __xfrm_decode_session 19 19 377d 398d 0/2 auto-obsoleted due to no activity on 2025/10/01 05:45
linux-5.15 KASAN: slab-out-of-bounds Read in __xfrm_decode_session (3) origin:lts-only 19 syz, C error 11 50d 114d 0/3 upstream: reported C repro on 2026/04/11 21:07
linux-6.1 KASAN: use-after-free Read in __xfrm_decode_session (2) origin:lts-only 19 syz, C inconclusive 9 251d 460d 0/3 upstream: reported C repro on 2025/04/30 13:03
upstream KASAN: slab-out-of-bounds Read in __xfrm_decode_session (2) net 19 7 1702d 1939d 0/29 auto-closed as invalid on 2022/04/04 17:22
upstream KMSAN: kernel-infoleak in copyout (2) net 17 syz, C 6723 1153d 2321d 22/29 fixed on 2023/06/08 14:41
linux-5.15 KASAN: slab-out-of-bounds Read in __xfrm_decode_session origin:upstream 19 syz, C error 7 999d 1186d 0/3 auto-obsoleted due to no activity on 2024/02/16 23:16
linux-6.1 KASAN: slab-out-of-bounds Read in __xfrm_decode_session 17 1 585d 585d 0/3 auto-obsoleted due to no activity on 2025/04/05 09:29
linux-5.15 KASAN: slab-out-of-bounds Read in __xfrm_decode_session (2) 19 4 363d 491d 0/3 auto-obsoleted due to no activity on 2025/11/13 13:37
upstream KASAN: slab-out-of-bounds Read in __xfrm_decode_session net 17 20 2154d 2439d 0/29 auto-closed as invalid on 2021/01/07 14:52
linux-6.1 KASAN: use-after-free Read in __xfrm_decode_session 19 4 1045d 1176d 0/3 auto-obsoleted due to no activity on 2024/01/01 21:03
linux-6.6 KASAN: slab-use-after-free Read in __xfrm_decode_session (2) 19 1 267d 267d 0/2 auto-obsoleted due to no activity on 2026/02/17 15:57
upstream KMSAN: kernel-infoleak in _copy_to_iter (7) net 21 syz, C 138977 1256d 1608d 22/29 fixed on 2023/02/24 13:50
upstream KMSAN: uninit-value in __xfrm_decode_session (4) net 19 syz, C 8 1016d 1063d 0/29 closed as invalid on 2023/12/14 11:46
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/04/26 05:47 13m fix candidate upstream error job log
2026/03/23 20:20 1m fix candidate upstream error job log

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in decode_session6 net/xfrm/xfrm_policy.c:3494 [inline]
BUG: KASAN: slab-out-of-bounds in __xfrm_decode_session+0x18d7/0x20a0 net/xfrm/xfrm_policy.c:3600
Read of size 1 at addr ffff8880780b2ff8 by task syz.0.17/5921

CPU: 0 PID: 5921 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 decode_session6 net/xfrm/xfrm_policy.c:3494 [inline]
 __xfrm_decode_session+0x18d7/0x20a0 net/xfrm/xfrm_policy.c:3600
 xfrm_decode_session_reverse include/net/xfrm.h:1237 [inline]
 icmpv6_route_lookup+0x442/0x600 net/ipv6/icmp.c:392
 icmp6_send+0x11a2/0x1b40 net/ipv6/icmp.c:604
 __icmpv6_send include/linux/icmpv6.h:28 [inline]
 icmpv6_send include/linux/icmpv6.h:49 [inline]
 ip6_link_failure+0x3b/0x4c0 net/ipv6/route.c:2835
 dst_link_failure include/net/dst.h:437 [inline]
 ip6_tnl_xmit+0xe8b/0x2a80 net/ipv6/ip6_tunnel.c:1282
 ipxip6_tnl_xmit net/ipv6/ip6_tunnel.c:1398 [inline]
 ip6_tnl_start_xmit+0xc6c/0x11c0 net/ipv6/ip6_tunnel.c:1446
 __netdev_start_xmit include/linux/netdevice.h:4943 [inline]
 netdev_start_xmit include/linux/netdevice.h:4957 [inline]
 xmit_one net/core/dev.c:3632 [inline]
 dev_hard_start_xmit+0x246/0x740 net/core/dev.c:3648
 sch_direct_xmit+0x25e/0x4c0 net/sched/sch_generic.c:345
 qdisc_restart net/sched/sch_generic.c:410 [inline]
 __qdisc_run+0xa56/0x1500 net/sched/sch_generic.c:418
 __dev_xmit_skb net/core/dev.c:3932 [inline]
 __dev_queue_xmit+0x10ad/0x3660 net/core/dev.c:4404
 neigh_output include/net/neighbour.h:543 [inline]
 ip6_finish_output2+0xe3d/0x1630 net/ipv6/ip6_output.c:141
 ip6_fragment+0x1535/0x1fd0 net/ipv6/ip6_output.c:1023
 dst_output include/net/dst.h:467 [inline]
 NF_HOOK include/linux/netfilter.h:304 [inline]
 ip6_xmit+0x10f1/0x1890 net/ipv6/ip6_output.c:360
 sctp_v6_xmit+0x9a4/0x1200 net/sctp/ipv6.c:250
 sctp_packet_transmit+0x247d/0x2a30 net/sctp/output.c:653
 sctp_packet_singleton+0x235/0x340 net/sctp/outqueue.c:783
 sctp_outq_flush_ctrl net/sctp/outqueue.c:914 [inline]
 sctp_outq_flush+0x50e/0x3120 net/sctp/outqueue.c:1212
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1198 [inline]
 sctp_do_sm+0x533b/0x5a60 net/sctp/sm_sideeffect.c:1169
 sctp_primitive_ASSOCIATE+0x95/0xc0 net/sctp/primitive.c:73
 sctp_sendmsg_to_asoc+0x10a6/0x1830 net/sctp/socket.c:1839
 sctp_sendmsg+0x1b83/0x28c0 net/sctp/socket.c:2029
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 __sys_sendto+0x4a9/0x6b0 net/socket.c:2200
 __do_sys_sendto net/socket.c:2212 [inline]
 __se_sys_sendto net/socket.c:2208 [inline]
 __x64_sys_sendto+0xde/0xf0 net/socket.c:2208
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd11b99c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeaaa454a8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007fd11bc15fa0 RCX: 00007fd11b99c799
RDX: 0000000000000001 RSI: 0000200000000240 RDI: 0000000000000005
RBP: 00007fd11ba32c99 R08: 0000200000000080 R09: 000000000000001c
R10: 0000000000000051 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd11bc15fac R14: 00007fd11bc15fa0 R15: 00007fd11bc15fa0
 </TASK>

The buggy address belongs to the object at ffff8880780b2000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 2040 bytes to the right of
 allocated 2048-byte region [ffff8880780b2000, ffff8880780b2800)

The buggy address belongs to the physical page:
page:ffffea0001e02c00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x780b0
head:ffffea0001e02c00 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c42000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 5921, tgid 5921 (syz.0.17), ts 96101012200, free_ts 95968154510
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1581
 prep_new_page mm/page_alloc.c:1588 [inline]
 get_page_from_freelist+0x1951/0x19e0 mm/page_alloc.c:3220
 __alloc_pages+0x1f0/0x460 mm/page_alloc.c:4500
 alloc_slab_page+0x5d/0x160 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:2081
 ___slab_alloc+0xc5d/0x12f0 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 __kmem_cache_alloc_node+0x19e/0x250 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc_node_track_caller+0xa2/0x230 mm/slab_common.c:1027
 kmalloc_reserve+0x116/0x240 net/core/skbuff.c:584
 pskb_expand_head+0x185/0x1230 net/core/skbuff.c:2103
 nf_nat_icmpv6_reply_translation+0x144/0xa00 net/netfilter/nf_nat_proto.c:853
 nf_nat_ipv6_fn+0x1f6/0x2e0 net/netfilter/nf_nat_proto.c:928
 nf_nat_ipv6_in+0xfd/0x2b0 net/netfilter/nf_nat_proto.c:947
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_slow+0xbd/0x200 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:259 [inline]
 NF_HOOK+0x21d/0x3b0 include/linux/netfilter.h:302
 __netif_receive_skb_one_core net/core/dev.c:5634 [inline]
 __netif_receive_skb+0xcc/0x290 net/core/dev.c:5748
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1181 [inline]
 free_unref_page_prepare+0x7b2/0x8c0 mm/page_alloc.c:2365
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2458
 discard_slab mm/slub.c:2127 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
 put_cpu_partial+0x17c/0x250 mm/slub.c:2743
 __slab_free+0x319/0x400 mm/slub.c:3700
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4b0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 kmem_cache_alloc_node+0x14c/0x320 mm/slub.c:3540
 __alloc_skb+0x103/0x2c0 net/core/skbuff.c:643
 alloc_skb include/linux/skbuff.h:1316 [inline]
 nlmsg_new include/net/netlink.h:1010 [inline]
 mpls_netconf_notify_devconf+0x46/0xf0 net/mpls/af_mpls.c:1189
 mpls_dev_notify+0x533/0x7a0 net/mpls/af_mpls.c:1643
 notifier_call_chain+0x197/0x380 kernel/notifier.c:93
 call_netdevice_notifiers_extack net/core/dev.c:2077 [inline]
 call_netdevice_notifiers net/core/dev.c:2091 [inline]
 unregister_netdevice_many_notify+0x100d/0x1900 net/core/dev.c:11112
 ip6gre_exit_batch_net+0x451/0x4a0 net/ipv6/ip6_gre.c:1654

Memory state around the buggy address:
 ffff8880780b2e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880780b2f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880780b2f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                                ^
 ffff8880780b3000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880780b3080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/22 10:20 linux-6.6.y 4fc00fe35d46 5b92003d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
* Struck through repros no longer work on HEAD.