KASAN: slab-use-after-free Read in __ip6_del_rt

Status: auto-obsoleted due to no activity on 2025/11/27 23:21
Reported-by: syzbot+dda2170a0d62642b3b22@syzkaller.appspotmail.com
First crash: 365d, last: 365d
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Write in __ip6_del_rt 22 syz 11 335d 485d 0/2 auto-obsoleted due to no activity on 2025/12/18 13:03
android-5-15 KASAN: use-after-free Write in __ip6_del_rt 22 1 472d 472d 0/2 auto-obsoleted due to no activity on 2025/08/03 14:28
android-6-1 KASAN: use-after-free Write in __ip6_del_rt origin:lts 22 syz error 1 296d 296d 0/2 auto-obsoleted due to no activity on 2026/01/26 10:27
linux-5.15 KASAN: use-after-free Read in __ip6_del_rt 19 1 510d 510d 0/3 auto-obsoleted due to no activity on 2025/07/06 21:22

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in __lock_acquire+0xff/0x7c80 kernel/locking/lockdep.c:5005
Read of size 8 at addr ffff888030901c30 by task kworker/u4:15/11340

CPU: 1 PID: 11340 Comm: kworker/u4:15 Not tainted 6.6.102-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: netns cleanup_net
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xac/0x220 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 __lock_acquire+0xff/0x7c80 kernel/locking/lockdep.c:5005
 lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:356 [inline]
 __ip6_del_rt+0x8c/0x150 net/ipv6/route.c:3911
 ip6_del_rt+0xb4/0x100 net/ipv6/route.c:3927
 __remove_nexthop_fib net/ipv4/nexthop.c:1884 [inline]
 __remove_nexthop+0x282/0x1a60 net/ipv4/nexthop.c:1892
 remove_nexthop+0x6f/0x170 net/ipv4/nexthop.c:1918
 remove_nh_grp_entry net/ipv4/nexthop.c:1774 [inline]
 remove_nexthop_from_groups net/ipv4/nexthop.c:1839 [inline]
 __remove_nexthop+0x99b/0x1a60 net/ipv4/nexthop.c:1903
 remove_nexthop+0x6f/0x170 net/ipv4/nexthop.c:1918
 flush_all_nexthops net/ipv4/nexthop.c:2427 [inline]
 nexthop_net_exit_batch+0x71/0x120 net/ipv4/nexthop.c:3747
 ops_exit_list net/core/net_namespace.c:178 [inline]
 cleanup_net+0x77f/0xb90 net/core/net_namespace.c:652
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>

Allocated by task 16959:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 fib6_net_init+0x20c/0x810 net/ipv6/ip6_fib.c:2388
 ops_init+0x397/0x640 net/core/net_namespace.c:139
 setup_net+0x3a5/0xa00 net/core/net_namespace.c:343
 copy_net_ns+0x36d/0x5e0 net/core/net_namespace.c:520
 create_new_namespaces+0x3d3/0x6f0 kernel/nsproxy.c:110
 unshare_nsproxy_namespaces+0x11a/0x160 kernel/nsproxy.c:228
 ksys_unshare+0x4c0/0x890 kernel/fork.c:3439
 __do_sys_unshare kernel/fork.c:3510 [inline]
 __se_sys_unshare kernel/fork.c:3508 [inline]
 __x64_sys_unshare+0x38/0x40 kernel/fork.c:3508
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 11340:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:522
 ____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1806 [inline]
 slab_free_freelist_hook+0x130/0x1b0 mm/slub.c:1832
 slab_free mm/slub.c:3816 [inline]
 __kmem_cache_free+0xba/0x1f0 mm/slub.c:3829
 fib6_free_table net/ipv6/ip6_fib.c:215 [inline]
 fib6_net_exit+0x26c/0x300 net/ipv6/ip6_fib.c:2442
 ops_exit_list net/core/net_namespace.c:173 [inline]
 cleanup_net+0x6f4/0xb90 net/core/net_namespace.c:652
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:45
 __kasan_record_aux_stack+0xaf/0xc0 mm/kasan/generic.c:492
 __call_rcu_common kernel/rcu/tree.c:2721 [inline]
 call_rcu+0x158/0x930 kernel/rcu/tree.c:2837
 kthread_worker_fn+0x4d4/0xa90 kernel/kthread.c:843
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Second to last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:45
 __kasan_record_aux_stack+0xaf/0xc0 mm/kasan/generic.c:492
 insert_work+0x3d/0x310 kernel/workqueue.c:1651
 __queue_work+0xd2c/0x1020 kernel/workqueue.c:1804
 call_timer_fn+0x16e/0x530 kernel/time/timer.c:1700
 expire_timers kernel/time/timer.c:1746 [inline]
 __run_timers+0x558/0x7d0 kernel/time/timer.c:2022
 run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2035
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xc7/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687

The buggy address belongs to the object at ffff888030901c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 48 bytes inside of
 freed 512-byte region [ffff888030901c00, ffff888030901e00)

The buggy address belongs to the physical page:
page:ffffea0000c24000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x30900
head:ffffea0000c24000 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017841c80 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 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 4708, tgid 4708 (kworker/u4:5), ts 17109342848, free_ts 0
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
 prep_new_page mm/page_alloc.c:1561 [inline]
 get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
 __alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
 alloc_slab_page+0x5d/0x170 mm/slub.c:1876
 allocate_slab mm/slub.c:2023 [inline]
 new_slab+0x87/0x2e0 mm/slub.c:2076
 ___slab_alloc+0xc6d/0x12f0 mm/slub.c:3230
 __slab_alloc mm/slub.c:3329 [inline]
 __slab_alloc_node mm/slub.c:3382 [inline]
 slab_alloc_node mm/slub.c:3475 [inline]
 __kmem_cache_alloc_node+0x1a2/0x260 mm/slub.c:3524
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 alloc_bprm+0x56/0x9c0 fs/exec.c:1538
 kernel_execve+0x98/0x9c0 fs/exec.c:2023
 call_usermodehelper_exec_async+0x20b/0x350 kernel/umh.c:110
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888030901b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888030901b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888030901c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                     ^
 ffff888030901c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888030901d00: 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
2025/08/19 23:21 linux-6.6.y bb9c90ab9c5a 254a27c1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in __ip6_del_rt
* Struck through repros no longer work on HEAD.