KASAN: slab-out-of-bounds Read in __xfrm_decode_session (3)

Status: upstream: reported C repro on 2026/04/11 21:07
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+45602763b68b48e65f94@syzkaller.appspotmail.com
First crash: 114d, last: 51d
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/04/12 linux-5.15.y (ToT) 91d48252ad4b C [report] KASAN: use-after-free Read in __xfrm_decode_session
2026/04/12 upstream (ToT) f5459048c38a C Didn't crash
▶ ▼ Similar bugs (14)
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-6.1 KASAN: use-after-free Read in __xfrm_decode_session (2) origin:lts-only 19 syz, C inconclusive 9 251d 461d 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-6.6 KASAN: slab-out-of-bounds Read in __xfrm_decode_session origin:lts-only 17 syz, C error 1 134d 135d 0/2 upstream: reported C repro on 2026/03/22 10:21
linux-6.1 KASAN: slab-out-of-bounds Read in __xfrm_decode_session 17 1 586d 586d 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 364d 492d 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 2440d 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 1177d 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 1257d 1609d 22/29 fixed on 2023/02/24 13:50
upstream KMSAN: uninit-value in __xfrm_decode_session (4) net 19 syz, C 8 1017d 1064d 0/29 closed as invalid on 2023/12/14 11:46
upstream KASAN: use-after-free Read in __xfrm_decode_session net 19 12 2159d 2518d 0/29 auto-closed as invalid on 2021/01/03 02:25
▶ ▼ Last patch testing requests (7)
Created Duration User Patch Repo Result
2026/06/01 06:20 16m retest repro linux-5.15.y report log
2026/06/01 06:20 24m retest repro linux-5.15.y report log
2026/05/16 03:19 19m retest repro linux-5.15.y report log
2026/05/16 03:19 19m retest repro linux-5.15.y report log
2026/05/16 03:19 16m retest repro linux-5.15.y report log
2026/05/16 03:19 32m retest repro linux-5.15.y report log
2026/05/16 03:19 50m retest repro linux-5.15.y report log
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
2026/04/12 05:59 1m fix candidate upstream error job log

Sample crash report:
netlink: 80 bytes leftover after parsing attributes in process `syz.0.18'.
==================================================================
BUG: KASAN: slab-out-of-bounds in decode_session6 net/xfrm/xfrm_policy.c:3413 [inline]
BUG: KASAN: slab-out-of-bounds in __xfrm_decode_session+0x17ae/0x1fa0 net/xfrm/xfrm_policy.c:3520
Read of size 1 at addr ffff888072c3abc7 by task syz.0.18/4316

CPU: 0 PID: 4316 Comm: syz.0.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 decode_session6 net/xfrm/xfrm_policy.c:3413 [inline]
 __xfrm_decode_session+0x17ae/0x1fa0 net/xfrm/xfrm_policy.c:3520
 xfrm_decode_session_reverse include/net/xfrm.h:1170 [inline]
 icmpv6_route_lookup+0x3ea/0x5a0 net/ipv6/icmp.c:394
 icmp6_send+0xff2/0x1990 net/ipv6/icmp.c:601
 __icmpv6_send include/linux/icmpv6.h:28 [inline]
 icmpv6_send include/linux/icmpv6.h:49 [inline]
 ip6_link_failure+0x35/0x490 net/ipv6/route.c:2788
 dst_link_failure include/net/dst.h:422 [inline]
 ip6_tnl_xmit+0x671/0x23e0 net/ipv6/ip6_tunnel.c:1274
 ipxip6_tnl_xmit net/ipv6/ip6_tunnel.c:1390 [inline]
 ip6_tnl_start_xmit+0xd27/0x12d0 net/ipv6/ip6_tunnel.c:1439
 __netdev_start_xmit include/linux/netdevice.h:5036 [inline]
 netdev_start_xmit include/linux/netdevice.h:5050 [inline]
 xmit_one net/core/dev.c:3662 [inline]
 dev_hard_start_xmit+0x2a5/0x7e0 net/core/dev.c:3678
 sch_direct_xmit+0x25a/0x4b0 net/sched/sch_generic.c:345
 qdisc_restart net/sched/sch_generic.c:410 [inline]
 __qdisc_run+0xa7e/0x1490 net/sched/sch_generic.c:418
 __dev_xmit_skb net/core/dev.c:3955 [inline]
 __dev_queue_xmit+0xe3d/0x2f80 net/core/dev.c:4266
 neigh_output include/net/neighbour.h:509 [inline]
 ip6_finish_output2+0x108c/0x1510 net/ipv6/ip6_output.c:130
 ip6_fragment+0x133d/0x1ee0 net/ipv6/ip6_output.c:998
 dst_output include/net/dst.h:452 [inline]
 NF_HOOK include/linux/netfilter.h:302 [inline]
 ip6_xmit+0x109b/0x16d0 net/ipv6/ip6_output.c:338
 sctp_v6_xmit+0x985/0x11b0 net/sctp/ipv6.c:250
 sctp_packet_transmit+0x239c/0x2910 net/sctp/output.c:652
 sctp_packet_singleton+0x231/0x330 net/sctp/outqueue.c:780
 sctp_outq_flush_ctrl net/sctp/outqueue.c:911 [inline]
 sctp_outq_flush+0x4ac/0x3100 net/sctp/outqueue.c:1209
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1199 [inline]
 sctp_do_sm+0x4ee2/0x55f0 net/sctp/sm_sideeffect.c:1170
 sctp_primitive_ASSOCIATE+0x91/0xc0 net/sctp/primitive.c:73
 sctp_sendmsg_to_asoc+0x14a7/0x1d90 net/sctp/socket.c:1840
 sctp_sendmsg+0x196a/0x2900 net/sctp/socket.c:2030
 sock_sendmsg_nosec net/socket.c:706 [inline]
 __sock_sendmsg net/socket.c:718 [inline]
 ____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2499
 __sys_sendmmsg+0x2ba/0x500 net/socket.c:2585
 __do_sys_sendmmsg net/socket.c:2614 [inline]
 __se_sys_sendmmsg net/socket.c:2611 [inline]
 __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2611
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fe159197819
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:00007ffc1d6244a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007fe159410fa0 RCX: 00007fe159197819
RDX: 0000000000000002 RSI: 0000200000002fc0 RDI: 0000000000000004
RBP: 00007fe15922dc91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000024000045 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe159410fac R14: 00007fe159410fa0 R15: 00007fe159410fa0
 </TASK>

Allocated by task 4316:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xb5/0xf0 mm/kasan/common.c:522
 kmalloc_reserve net/core/skbuff.c:356 [inline]
 __alloc_skb+0x22c/0x750 net/core/skbuff.c:427
 alloc_skb include/linux/skbuff.h:1162 [inline]
 ip6_frag_next+0x128/0xbb0 net/ipv6/ip6_output.c:777
 ip6_fragment+0x12ee/0x1ee0 net/ipv6/ip6_output.c:988
 dst_output include/net/dst.h:452 [inline]
 NF_HOOK include/linux/netfilter.h:302 [inline]
 ip6_xmit+0x109b/0x16d0 net/ipv6/ip6_output.c:338
 sctp_v6_xmit+0x985/0x11b0 net/sctp/ipv6.c:250
 sctp_packet_transmit+0x239c/0x2910 net/sctp/output.c:652
 sctp_packet_singleton+0x231/0x330 net/sctp/outqueue.c:780
 sctp_outq_flush_ctrl net/sctp/outqueue.c:911 [inline]
 sctp_outq_flush+0x4ac/0x3100 net/sctp/outqueue.c:1209
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1199 [inline]
 sctp_do_sm+0x4ee2/0x55f0 net/sctp/sm_sideeffect.c:1170
 sctp_primitive_ASSOCIATE+0x91/0xc0 net/sctp/primitive.c:73
 sctp_sendmsg_to_asoc+0x14a7/0x1d90 net/sctp/socket.c:1840
 sctp_sendmsg+0x196a/0x2900 net/sctp/socket.c:2030
 sock_sendmsg_nosec net/socket.c:706 [inline]
 __sock_sendmsg net/socket.c:718 [inline]
 ____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2499
 __sys_sendmmsg+0x2ba/0x500 net/socket.c:2585
 __do_sys_sendmmsg net/socket.c:2614 [inline]
 __se_sys_sendmmsg net/socket.c:2611 [inline]
 __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2611
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff888072c3a000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 967 bytes to the right of
 2048-byte region [ffff888072c3a000, ffff888072c3a800)
The buggy address belongs to the page:
page:ffffea0001cb0e00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x72c38
head:ffffea0001cb0e00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888016c42000
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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4316, ts 84473716433, free_ts 84451446553
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x1bbd/0x1ca0 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x80a/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 __kmalloc+0x1cd/0x330 mm/slub.c:4408
 kmalloc include/linux/slab.h:612 [inline]
 sk_prot_alloc+0xe7/0x210 net/core/sock.c:1866
 sk_alloc+0x2f/0x310 net/core/sock.c:1922
 __netlink_create+0x6b/0x2d0 net/netlink/af_netlink.c:629
 netlink_create+0x3a7/0x510 net/netlink/af_netlink.c:692
 __sock_create+0x47b/0x900 net/socket.c:1495
 sock_create net/socket.c:1551 [inline]
 __sys_socket+0xe2/0x170 net/socket.c:1593
 __do_sys_socket net/socket.c:1602 [inline]
 __se_sys_socket net/socket.c:1600 [inline]
 __x64_sys_socket+0x76/0x80 net/socket.c:1600
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 free_slab mm/slub.c:2020 [inline]
 discard_slab mm/slub.c:2026 [inline]
 __unfreeze_partials+0x1a5/0x200 mm/slub.c:2512
 put_cpu_partial+0x12d/0x190 mm/slub.c:2592
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xd0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x100/0x290 mm/slub.c:3238
 getname_flags+0xb5/0x500 fs/namei.c:138
 getname fs/namei.c:217 [inline]
 __do_sys_unlink fs/namei.c:4404 [inline]
 __se_sys_unlink fs/namei.c:4402 [inline]
 __x64_sys_unlink+0x38/0x50 fs/namei.c:4402
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Memory state around the buggy address:
 ffff888072c3aa80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888072c3ab00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888072c3ab80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                           ^
 ffff888072c3ac00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888072c3ac80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (11):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/12 14:16 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/04/12 09:49 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/04/12 06:34 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/04/12 01:45 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/04/11 23:28 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/04/12 16:52 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in __xfrm_decode_session
2026/04/12 12:05 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in __xfrm_decode_session
2026/04/12 04:16 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in __xfrm_decode_session
2026/06/14 13:29 linux-5.15.y dc027a595035 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/06/07 11:19 linux-5.15.y dc027a595035 cc095639 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
2026/04/11 21:06 linux-5.15.y 91d48252ad4b 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: slab-out-of-bounds Read in __xfrm_decode_session
* Struck through repros no longer work on HEAD.