KASAN: use-after-free Read in __ipv6_addr_type

Status: upstream: reported C repro on 2026/10/04 22:38
Reported-by: syzbot+0abe196b96d296a7c078@syzkaller.appspotmail.com
First crash: 5d06h, last: 5d06h
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: use-after-free Read in __ipv6_addr_type origin:lts 19 syz, C 6 23d 23d 0/2 upstream: reported C repro on 2026/09/16 12:02
upstream KASAN: use-after-free Read in __ipv6_addr_type net 19 1 2849d 2849d 11/29 fixed on 2019/01/11 01:22
upstream KMSAN: kernel-infoleak in copyout (2) net 17 syz, C 6723 1220d 2388d 22/29 fixed on 2023/06/08 14:41
upstream KMSAN: uninit-value in __ipv6_addr_type net 7 syz, C 3 596d 596d 28/29 fixed on 2025/06/10 16:19
upstream KMSAN: kernel-infoleak in _copy_to_iter (7) net 21 syz, C 138977 1323d 1675d 22/29 fixed on 2023/02/24 13:50
upstream KMSAN: uninit-value in IP6_ECN_decapsulate net 7 syz, C 981 1025d 2941d 25/29 fixed on 2023/12/21 03:45

Sample crash report:
request_module fs-gadgetfs succeeded, but still no fs?
==================================================================
BUG: KASAN: use-after-free in __ipv6_addr_type+0x272/0x2f0 net/ipv6/addrconf_core.c:42
Read of size 4 at addr ffff88810cf7c048 by task syz-executor339/298

CPU: 0 PID: 298 Comm: syz-executor339 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x100/0x140 mm/kasan/report.c:452
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 __ipv6_addr_type+0x272/0x2f0 net/ipv6/addrconf_core.c:42
 ipv6_addr_type include/net/ipv6.h:464 [inline]
 ip6_forward+0xe70/0x1ae0 net/ipv6/ip6_output.c:590
 dst_input include/net/dst.h:461 [inline]
 ip6_rcv_finish+0x18c/0x360 net/ipv6/ip6_input.c:80
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ipv6_rcv+0xf0/0x230 net/ipv6/ip6_input.c:301
 __netif_receive_skb_one_core net/core/dev.c:5413 [inline]
 __netif_receive_skb+0xc8/0x280 net/core/dev.c:5527
 netif_receive_skb_internal net/core/dev.c:5632 [inline]
 netif_receive_skb+0x9b/0x3e0 net/core/dev.c:5691
 tun_rx_batched+0x600/0x750 drivers/net/tun.c:-1
 tun_get_user+0x26f6/0x31a0 drivers/net/tun.c:2037
 tun_chr_write_iter+0x1c1/0x270 drivers/net/tun.c:2070
 call_write_iter include/linux/fs.h:2072 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x770/0xd70 fs/read_write.c:605
 ksys_write+0x14a/0x260 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f9798fe05c9
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeac8db9c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9799041500 RCX: 00007f9798fe05c9
RDX: 000000000000ffdd RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007f97990414d0 R08: 00007ffeac8db9f0 R09: 00007ffeac8db9f0
R10: 00007ffeac8db9f0 R11: 0000000000000246 R12: 00007f9799041438
R13: 0000000000000001 R14: 00007ffeac8dba20 R15: 0000000000000003

Allocated by task 0:
(stack is not available)

Freed by task 298:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kfree+0xc0/0x270 mm/slub.c:4196
 skb_free_head net/core/skbuff.c:606 [inline]
 pskb_expand_head+0x386/0x11c0 net/core/skbuff.c:1691
 __pskb_pull_tail+0xb2/0x1450 net/core/skbuff.c:2197
 pskb_may_pull include/linux/skbuff.h:2397 [inline]
 decode_session6 net/xfrm/xfrm_policy.c:3425 [inline]
 __xfrm_decode_session+0x591/0x2310 net/xfrm/xfrm_policy.c:3524
 xfrm_decode_session include/net/xfrm.h:1153 [inline]
 __xfrm_route_forward+0x10e/0x3d0 net/xfrm/xfrm_policy.c:3727
 xfrm_route_forward include/net/xfrm.h:1171 [inline]
 xfrm6_route_forward include/net/xfrm.h:1181 [inline]
 ip6_forward+0xd57/0x1ae0 net/ipv6/ip6_output.c:553
 dst_input include/net/dst.h:461 [inline]
 ip6_rcv_finish+0x18c/0x360 net/ipv6/ip6_input.c:80
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ipv6_rcv+0xf0/0x230 net/ipv6/ip6_input.c:301
 __netif_receive_skb_one_core net/core/dev.c:5413 [inline]
 __netif_receive_skb+0xc8/0x280 net/core/dev.c:5527
 netif_receive_skb_internal net/core/dev.c:5632 [inline]
 netif_receive_skb+0x9b/0x3e0 net/core/dev.c:5691
 tun_rx_batched+0x600/0x750 drivers/net/tun.c:-1
 tun_get_user+0x26f6/0x31a0 drivers/net/tun.c:2037
 tun_chr_write_iter+0x1c1/0x270 drivers/net/tun.c:2070
 call_write_iter include/linux/fs.h:2072 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x770/0xd70 fs/read_write.c:605
 ksys_write+0x14a/0x260 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

The buggy address belongs to the object at ffff88810cf7c000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 72 bytes inside of
 512-byte region [ffff88810cf7c000, ffff88810cf7c200)
The buggy address belongs to the page:
page:ffffea000433df00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10cf7c
head:ffffea000433df00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 298, ts 24005561133, free_ts 24005511770
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x176/0x190 mm/page_alloc.c:2462
 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 __kmalloc+0x1f9/0x330 mm/slub.c:4034
 kmalloc include/linux/slab.h:560 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 fib6_info_alloc+0x34/0xe0 net/ipv6/ip6_fib.c:154
 ip6_route_info_create+0x4c7/0x1450 net/ipv6/route.c:3671
 addrconf_f6i_alloc+0x19c/0x3f0 net/ipv6/route.c:4470
 ipv6_add_addr+0x442/0xd90 net/ipv6/addrconf.c:1119
 addrconf_add_linklocal+0x209/0x660 net/ipv6/addrconf.c:3263
 addrconf_addr_gen+0x51c/0x6a0 net/ipv6/addrconf.c:3382
 addrconf_dev_config+0x299/0x510 net/ipv6/addrconf.c:3446
 addrconf_notify+0x9d8/0xea0 net/ipv6/addrconf.c:3679
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629
 free_the_page mm/page_alloc.c:5445 [inline]
 __free_pages+0xd8/0x390 mm/page_alloc.c:5454
 free_pages+0x82/0x90 mm/page_alloc.c:5465
 __stack_depot_save+0x492/0x4c0 lib/stackdepot.c:359
 kasan_save_stack mm/kasan/common.c:39 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:430 [inline]
 ____kasan_kmalloc mm/kasan/common.c:509 [inline]
 __kasan_kmalloc+0xe6/0x100 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 __kmalloc+0x19f/0x330 mm/slub.c:4038
 kmalloc include/linux/slab.h:560 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 fib6_info_alloc+0x34/0xe0 net/ipv6/ip6_fib.c:154
 ip6_route_info_create+0x4c7/0x1450 net/ipv6/route.c:3671
 ip6_route_add+0x27/0x130 net/ipv6/route.c:3767
 addrconf_add_mroute net/ipv6/addrconf.c:2533 [inline]
 addrconf_add_dev+0x385/0x4c0 net/ipv6/addrconf.c:2551
 addrconf_dev_config+0x1c3/0x510 net/ipv6/addrconf.c:3433
 addrconf_notify+0x9d8/0xea0 net/ipv6/addrconf.c:3679
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410
 call_netdevice_notifiers_info net/core/dev.c:2052 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2064 [inline]
 call_netdevice_notifiers net/core/dev.c:2078 [inline]
 __dev_notify_flags+0x2f4/0x5b0 net/core/dev.c:8583
 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8621
 dev_ifsioc+0x113/0xa90 net/core/dev_ioctl.c:230

Memory state around the buggy address:
 ffff88810cf7bf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810cf7bf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810cf7c000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff88810cf7c080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810cf7c100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/04 22:38 android13-5.10-lts 42d4fb705937 57bbd979 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in __ipv6_addr_type
* Struck through repros no longer work on HEAD.