================================================================== BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75 Read of size 8 at addr ffff888116216990 by task syz.2.1097/4127 CPU: 1 PID: 4127 Comm: syz.2.1097 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026 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_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309 rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75 rcu_do_batch+0x448/0xaf0 kernel/rcu/tree.c:2484 rcu_core+0x50a/0xca0 kernel/rcu/tree.c:2735 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748 __do_softirq+0x255/0x563 kernel/softirq.c:309 asm_call_irq_on_stack+0xf/0x20 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline] run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline] do_softirq_own_stack+0x60/0x80 arch/x86/kernel/irq_64.c:77 invoke_softirq kernel/softirq.c:405 [inline] __irq_exit_rcu+0x128/0x150 kernel/softirq.c:435 irq_exit_rcu+0x9/0x10 kernel/softirq.c:447 sysvec_apic_timer_interrupt+0xbf/0xe0 arch/x86/kernel/apic/apic.c:1106 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:635 RIP: 0010:mark_buffer_dirty_inode+0x6/0x300 fs/buffer.c:573 Code: 49 83 c6 08 e9 23 fe ff ff e8 96 56 af ff eb 05 e8 8f 56 af ff 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 55 48 89 e5 41 57 <41> 56 41 55 41 54 53 48 83 ec 30 49 89 f6 49 89 ff 49 bc 00 00 00 RSP: 0018:ffffc90001de7358 EFLAGS: 00000246 RAX: 1ffff920003bce96 RBX: ffffc90001de74b0 RCX: 0000000000080000 RDX: ffffc90003d24000 RSI: ffff88812b5dd400 RDI: ffff888132d4a150 RBP: ffffc90001de7360 R08: ffffea00055bab47 R09: 1ffffd4000ab7568 R10: dffffc0000000000 R11: fffff94000ab7569 R12: dffffc0000000000 R13: 0000000000000003 R14: ffff888132d4a150 R15: ffff888156ead8d8 fat16_ent_put+0x91/0xb0 fs/fat/fatent.c:183 fat_alloc_clusters+0x4ac/0xde0 fs/fat/fatent.c:502 fat_add_cluster fs/fat/inode.c:108 [inline] __fat_get_block fs/fat/inode.c:155 [inline] fat_get_block+0x387/0x950 fs/fat/inode.c:190 __block_write_begin_int+0x502/0x15a0 fs/buffer.c:2042 __block_write_begin fs/buffer.c:2092 [inline] block_write_begin fs/buffer.c:2151 [inline] cont_write_begin+0x604/0x8b0 fs/buffer.c:2500 fat_write_begin+0xa0/0x170 fs/fat/inode.c:235 generic_perform_write+0x2ce/0x540 mm/filemap.c:3509 __generic_file_write_iter+0x24b/0x480 mm/filemap.c:3638 generic_file_write_iter+0xa9/0x1d0 mm/filemap.c:3670 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: 0033:0x7fb1c3b88f19 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:00007fb1c25d7028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007fb1c3e05fa0 RCX: 00007fb1c3b88f19 RDX: 00000000fffffdab RSI: 0000200000003b80 RDI: 0000000000000004 RBP: 00007fb1c3c17f6d R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fb1c3e06038 R14: 00007fb1c3e05fa0 R15: 00007ffc2f6b8458 Allocated by task 4129: 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:430 [inline] ____kasan_kmalloc mm/kasan/common.c:509 [inline] __kasan_kmalloc+0xd4/0x100 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] l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1616 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:772 __sys_connect_file net/socket.c:1867 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1884 __do_sys_connect net/socket.c:1894 [inline] __se_sys_connect net/socket.c:1891 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1891 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 300: 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 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline] l2tp_session_put+0xb2/0x1a0 net/l2tp/l2tp_core.c:193 l2tp_session_delete+0x3a9/0x4a0 net/l2tp/l2tp_core.c:1589 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1235 [inline] l2tp_tunnel_del_work+0x180/0x3d0 net/l2tp/l2tp_core.c:1273 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 Last potentially related work creation: kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358 __call_rcu kernel/rcu/tree.c:2980 [inline] call_rcu+0x11a/0x1090 kernel/rcu/tree.c:3054 pppol2tp_release+0x1e3/0x2b0 net/l2tp/l2tp_ppp.c:447 __sock_release net/socket.c:597 [inline] sock_close+0xb8/0x200 net/socket.c:1287 __fput+0x2dc/0x730 fs/file_table.c:281 ____fput+0x15/0x20 fs/file_table.c:314 task_work_run+0x127/0x190 kernel/task_work.c:189 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:175 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:202 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:277 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb Second to last potentially related work creation: kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358 __call_rcu kernel/rcu/tree.c:2980 [inline] call_rcu+0x11a/0x1090 kernel/rcu/tree.c:3054 inetdev_destroy net/ipv4/devinet.c:330 [inline] inetdev_event+0x825/0x1010 net/ipv4/devinet.c:1612 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] unregister_netdevice_many+0x100e/0x19f0 net/core/dev.c:10779 default_device_exit_batch+0x35e/0x3c0 net/core/dev.c:11299 ops_exit_list net/core/net_namespace.c:190 [inline] cleanup_net+0x5fe/0xb80 net/core/net_namespace.c:609 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 The buggy address belongs to the object at ffff888116216800 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 400 bytes inside of 512-byte region [ffff888116216800, ffff888116216a00) The buggy address belongs to the page: page:ffffea0004588500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x116214 head:ffffea0004588500 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 467, ts 31616322191, free_ts 31575753233 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:3675 ip6_route_add+0x27/0x130 net/ipv6/route.c:3771 addrconf_add_mroute net/ipv6/addrconf.c:2534 [inline] addrconf_add_dev+0x385/0x4c0 net/ipv6/addrconf.c:2552 inet6_addr_add+0x1b2/0x970 net/ipv6/addrconf.c:2999 inet6_rtm_newaddr+0x6e1/0x9c0 net/ipv6/addrconf.c:4977 rtnetlink_rcv_msg+0x9e9/0xca0 net/core/rtnetlink.c:5622 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2508 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5640 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_slab+0xcf/0x190 mm/slub.c:1899 free_slab mm/slub.c:1914 [inline] discard_slab mm/slub.c:1920 [inline] unfreeze_partials+0x150/0x180 mm/slub.c:2415 put_cpu_partial+0xc1/0x180 mm/slub.c:2451 __slab_free+0x2c9/0x3a0 mm/slub.c:3100 do_slab_free mm/slub.c:3196 [inline] ___cache_free+0x10e/0x130 mm/slub.c:3215 qlink_free+0x50/0x90 mm/kasan/quarantine.c:157 qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176 kasan_quarantine_reduce+0x14a/0x160 mm/kasan/quarantine.c:283 __kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:440 kasan_slab_alloc include/linux/kasan.h:244 [inline] slab_post_alloc_hook+0x5d/0x2f0 mm/slab.h:580 slab_alloc_node mm/slub.c:2952 [inline] slab_alloc mm/slub.c:2960 [inline] kmem_cache_alloc+0x15a/0x2d0 mm/slub.c:2965 prepare_creds+0x2c/0x560 kernel/cred.c:261 access_override_creds fs/open.c:354 [inline] do_faccessat+0xe8/0x960 fs/open.c:418 __do_sys_faccessat2 fs/open.c:478 [inline] __se_sys_faccessat2 fs/open.c:475 [inline] __x64_sys_faccessat2+0x9a/0xb0 fs/open.c:475 Memory state around the buggy address: ffff888116216880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888116216900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888116216980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888116216a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888116216a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ================================================================== ---------------- Code disassembly (best guess): 0: 49 83 c6 08 add $0x8,%r14 4: e9 23 fe ff ff jmp 0xfffffe2c 9: e8 96 56 af ff call 0xffaf56a4 e: eb 05 jmp 0x15 10: e8 8f 56 af ff call 0xffaf56a4 15: 48 83 c4 10 add $0x10,%rsp 19: 5b pop %rbx 1a: 41 5c pop %r12 1c: 41 5d pop %r13 1e: 41 5e pop %r14 20: 41 5f pop %r15 22: 5d pop %rbp 23: c3 ret 24: 55 push %rbp 25: 48 89 e5 mov %rsp,%rbp 28: 41 57 push %r15 * 2a: 41 56 push %r14 <-- trapping instruction 2c: 41 55 push %r13 2e: 41 54 push %r12 30: 53 push %rbx 31: 48 83 ec 30 sub $0x30,%rsp 35: 49 89 f6 mov %rsi,%r14 38: 49 89 ff mov %rdi,%r15 3b: 49 rex.WB 3c: bc .byte 0xbc 3d: 00 00 add %al,(%rax)