KASAN: use-after-free Read in __ipv6_addr_type

Status: upstream: reported C repro on 2026/09/16 12:02
Reported-by: syzbot+9154a38789a5ff67b7d9@syzkaller.appspotmail.com
First crash: 5d07h, last: 4d17h
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: use-after-free Read in __ipv6_addr_type net 19 1 2831d 2831d 11/29 fixed on 2019/01/11 01:22
upstream KMSAN: kernel-infoleak in copyout (2) net 17 syz, C 6723 1201d 2369d 22/29 fixed on 2023/06/08 14:41
upstream KMSAN: uninit-value in __ipv6_addr_type net 7 syz, C 3 577d 577d 28/29 fixed on 2025/06/10 16:19
upstream KMSAN: kernel-infoleak in _copy_to_iter (7) net 21 syz, C 138977 1305d 1657d 22/29 fixed on 2023/02/24 13:50
upstream KMSAN: uninit-value in IP6_ECN_decapsulate net 7 syz, C 981 1006d 2922d 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 ffff88810cbc9848 by task syz-executor269/304

CPU: 0 PID: 304 Comm: syz-executor269 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0x10f/0x150 mm/kasan/report.c:444
 __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:465 [inline]
 ip6_forward+0xdb2/0x1ba0 net/ipv6/ip6_output.c:602
 dst_input include/net/dst.h:463 [inline]
 ip6_rcv_finish+0x18f/0x360 net/ipv6/ip6_input.c:79
 NF_HOOK include/linux/netfilter.h:305 [inline]
 ipv6_rcv+0xed/0x230 net/ipv6/ip6_input.c:300
 __netif_receive_skb_one_core net/core/dev.c:5559 [inline]
 __netif_receive_skb+0xc8/0x280 net/core/dev.c:5673
 netif_receive_skb_internal net/core/dev.c:5759 [inline]
 netif_receive_skb+0x98/0x3e0 net/core/dev.c:5818
 tun_rx_batched+0x600/0x750 drivers/net/tun.c:-1
 tun_get_user+0x284f/0x34c0 drivers/net/tun.c:1989
 tun_chr_write_iter+0x1ed/0x2f0 drivers/net/tun.c:2019
 call_write_iter include/linux/fs.h:2212 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x831/0xfd0 fs/read_write.c:594
 ksys_write+0x14a/0x260 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:656
 x64_sys_call+0x8ef/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 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: 0033:0x7f275c6815c9
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:00007ffe96b68928 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f275c6e2500 RCX: 00007f275c6815c9
RDX: 000000000000ffdd RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007f275c6e24d0 R08: 00007ffe96b68950 R09: 00007ffe96b68950
R10: 00007ffe96b68950 R11: 0000000000000246 R12: 00007f275c6e2438
R13: 0000000000000001 R14: 00007ffe96b68980 R15: 0000000000000003
 </TASK>

Allocated by task 304:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:433 [inline]
 ____kasan_kmalloc mm/kasan/common.c:512 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
 kasan_kmalloc include/linux/kasan.h:227 [inline]
 __kmalloc_track_caller+0x13c/0x2c0 mm/slub.c:4959
 kmalloc_reserve net/core/skbuff.c:357 [inline]
 __alloc_skb+0x210/0x730 net/core/skbuff.c:428
 alloc_skb include/linux/skbuff.h:1183 [inline]
 alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6220
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2541
 tun_alloc_skb drivers/net/tun.c:1510 [inline]
 tun_get_user+0xaa2/0x34c0 drivers/net/tun.c:1822
 tun_chr_write_iter+0x1ed/0x2f0 drivers/net/tun.c:2019
 call_write_iter include/linux/fs.h:2212 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x831/0xfd0 fs/read_write.c:594
 ksys_write+0x14a/0x260 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:656
 x64_sys_call+0x8ef/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 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

Freed by task 304:
 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:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 skb_free_head net/core/skbuff.c:656 [inline]
 pskb_expand_head+0x394/0x1280 net/core/skbuff.c:1767
 __pskb_pull_tail+0xba/0x1570 net/core/skbuff.c:2282
 pskb_may_pull include/linux/skbuff.h:2490 [inline]
 decode_session6 net/xfrm/xfrm_policy.c:3394 [inline]
 __xfrm_decode_session+0x5b0/0x1de0 net/xfrm/xfrm_policy.c:3488
 xfrm_decode_session include/net/xfrm.h:1166 [inline]
 __xfrm_route_forward+0x115/0x540 net/xfrm/xfrm_policy.c:3696
 xfrm_route_forward include/net/xfrm.h:1187 [inline]
 xfrm6_route_forward include/net/xfrm.h:1197 [inline]
 ip6_forward+0xca5/0x1ba0 net/ipv6/ip6_output.c:565
 dst_input include/net/dst.h:463 [inline]
 ip6_rcv_finish+0x18f/0x360 net/ipv6/ip6_input.c:79
 NF_HOOK include/linux/netfilter.h:305 [inline]
 ipv6_rcv+0xed/0x230 net/ipv6/ip6_input.c:300
 __netif_receive_skb_one_core net/core/dev.c:5559 [inline]
 __netif_receive_skb+0xc8/0x280 net/core/dev.c:5673
 netif_receive_skb_internal net/core/dev.c:5759 [inline]
 netif_receive_skb+0x98/0x3e0 net/core/dev.c:5818
 tun_rx_batched+0x600/0x750 drivers/net/tun.c:-1
 tun_get_user+0x284f/0x34c0 drivers/net/tun.c:1989
 tun_chr_write_iter+0x1ed/0x2f0 drivers/net/tun.c:2019
 call_write_iter include/linux/fs.h:2212 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x831/0xfd0 fs/read_write.c:594
 ksys_write+0x14a/0x260 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:656
 x64_sys_call+0x8ef/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 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 ffff88810cbc9800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 72 bytes inside of
 512-byte region [ffff88810cbc9800, ffff88810cbc9a00)
The buggy address belongs to the page:
page:ffffea000432f200 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88810cbcbc00 pfn:0x10cbc8
head:ffffea000432f200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004382000 0000000700000007 ffff888100042f00
raw: ffff88810cbcbc00 0000000080100006 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 102, ts 4705821674, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
 get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
 __alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1937 [inline]
 new_slab+0xa0/0x4d0 mm/slub.c:2000
 ___slab_alloc+0x3ac/0x840 mm/slub.c:3033
 __slab_alloc+0x49/0x90 mm/slub.c:3120
 slab_alloc_node mm/slub.c:3211 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 __kmalloc_track_caller+0x169/0x2c0 mm/slub.c:4954
 kmalloc_reserve net/core/skbuff.c:357 [inline]
 __alloc_skb+0x210/0x730 net/core/skbuff.c:428
 alloc_skb include/linux/skbuff.h:1183 [inline]
 alloc_uevent_skb+0x85/0x240 lib/kobject_uevent.c:290
 uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
 kobject_uevent_net_broadcast+0x335/0x5a0 lib/kobject_uevent.c:409
 kobject_uevent_env+0x52b/0x700 lib/kobject_uevent.c:608
 kobject_synth_uevent+0x457/0x940 lib/kobject_uevent.c:208
 uevent_store+0x4b/0x70 drivers/base/bus.c:583
 drv_attr_store+0x79/0xa0 drivers/base/bus.c:77
 sysfs_kf_write+0x129/0x150 fs/sysfs/file.c:143
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810cbc9700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810cbc9780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810cbc9800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff88810cbc9880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810cbc9900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/16 22:16 android13-5.15-lts 5bfe2b8c1439 12a0a44a .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in __ipv6_addr_type
2026/09/16 20:19 android13-5.15-lts 5bfe2b8c1439 12a0a44a .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in __ipv6_addr_type
2026/09/16 18:18 android13-5.15-lts 5bfe2b8c1439 12a0a44a .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in __ipv6_addr_type
2026/09/16 14:00 android13-5.15-lts 5bfe2b8c1439 12a0a44a .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in __ipv6_addr_type
2026/09/16 11:55 android13-5.15-lts 5bfe2b8c1439 12a0a44a .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in __ipv6_addr_type
2026/09/16 08:08 android13-5.15-lts 5bfe2b8c1439 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in __ipv6_addr_type
* Struck through repros no longer work on HEAD.