================================================================== BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75 Read of size 8 at addr ffff8881133d4990 by task syz.1.34/413 CPU: 0 PID: 413 Comm: syz.1.34 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 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:stack_trace_consume_entry+0xf8/0x290 kernel/stacktrace.c:92 Code: ff 48 8b 75 c0 4c 8b 37 45 8d 7a 01 0f b6 04 13 84 c0 0f 85 45 01 00 00 45 89 38 4f 8d 3c d6 4c 89 f8 48 c1 e8 03 80 3c 10 00 <74> 1e 4c 89 ff 49 89 d6 4d 89 c4 4c 89 cb e8 55 9b 4a 00 49 89 d9 RSP: 0018:ffffc90000cc6ad0 EFLAGS: 00000246 RAX: 1ffff92000198da3 RBX: 1ffff92000198d7e RCX: 0000000000198d01 RDX: dffffc0000000000 RSI: ffffffff84a000c5 RDI: ffffc90000cc6be0 RBP: ffffc90000cc6b18 R08: ffffc90000cc6bf0 R09: ffffc90000cc6be8 R10: 000000000000000f R11: fffff52000198d71 R12: ffffc90000cc6bec R13: 1ffff92000198d7d R14: ffffc90000cc6ca0 R15: ffffc90000cc6d18 arch_stack_walk+0xfc/0x140 arch/x86/kernel/stacktrace.c:27 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:121 save_stack+0xc1/0x230 mm/page_owner.c:146 __set_page_owner+0x3b/0x2a0 mm/page_owner.c:219 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_pages include/linux/gfp.h:544 [inline] __alloc_pages_node include/linux/gfp.h:557 [inline] alloc_pages_node include/linux/gfp.h:571 [inline] alloc_pages include/linux/gfp.h:590 [inline] shmem_alloc_page+0x1fd/0x380 mm/shmem.c:1580 shmem_alloc_and_acct_page+0x3d3/0x840 mm/shmem.c:1605 shmem_getpage_gfp+0x785/0x20f0 mm/shmem.c:1918 shmem_fault+0x2b5/0x650 mm/shmem.c:2139 __do_fault mm/memory.c:4064 [inline] do_read_fault mm/memory.c:4408 [inline] do_fault mm/memory.c:4536 [inline] handle_pte_fault+0x2466/0x3910 mm/memory.c:4800 __handle_mm_fault mm/memory.c:4953 [inline] handle_mm_fault+0xf86/0x1720 mm/memory.c:5367 faultin_page mm/gup.c:902 [inline] __get_user_pages+0xbf8/0x1400 mm/gup.c:1121 populate_vma_page_range mm/gup.c:1454 [inline] __mm_populate+0x31c/0x420 mm/gup.c:1502 mm_populate include/linux/mm.h:2793 [inline] vm_mmap_pgoff+0x23b/0x350 mm/util.c:548 ksys_mmap_pgoff+0xfd/0x1e0 mm/mmap.c:1712 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:95 [inline] __se_sys_mmap arch/x86/kernel/sys_x86_64.c:86 [inline] __x64_sys_mmap+0xfa/0x110 arch/x86/kernel/sys_x86_64.c:86 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f174c7a0019 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:00007f174b1f9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009 RAX: ffffffffffffffda RBX: 00007f174ca27fa0 RCX: 00007f174c7a0019 RDX: b635773f06ebbeee RSI: 0000000000b36000 RDI: 0000200000000000 RBP: 00007f174c83700c R08: ffffffffffffffff R09: 0000000000000000 R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f174ca28038 R14: 00007f174ca27fa0 R15: 00007ffed5de6458 Allocated by task 415: 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 49: 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:172 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb The buggy address belongs to the object at ffff8881133d4800 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 400 bytes inside of 512-byte region [ffff8881133d4800, ffff8881133d4a00) The buggy address belongs to the page: page:ffffea00044cf500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1133d4 head:ffffea00044cf500 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 ffffea00044cc300 0000000400000004 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 101, ts 7244343647, free_ts 0 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_track_caller+0x1e4/0x310 mm/slub.c:4541 __kmalloc_reserve net/core/skbuff.c:144 [inline] __alloc_skb+0xdc/0x520 net/core/skbuff.c:212 alloc_skb include/linux/skbuff.h:1126 [inline] alloc_skb_with_frags+0xa3/0x560 net/core/skbuff.c:6006 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2393 unix_dgram_sendmsg+0x6f3/0x18f0 net/unix/af_unix.c:1725 sock_sendmsg_nosec net/socket.c:652 [inline] __sock_sendmsg net/socket.c:664 [inline] sock_write_iter+0x2a6/0x3a0 net/socket.c:1019 call_write_iter include/linux/fs.h:2066 [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 page_owner free stack trace missing Memory state around the buggy address: ffff8881133d4880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881133d4900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff8881133d4980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8881133d4a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8881133d4a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ================================================================== ---------------- Code disassembly (best guess): 0: ff 48 8b decl -0x75(%rax) 3: 75 c0 jne 0xffffffc5 5: 4c 8b 37 mov (%rdi),%r14 8: 45 8d 7a 01 lea 0x1(%r10),%r15d c: 0f b6 04 13 movzbl (%rbx,%rdx,1),%eax 10: 84 c0 test %al,%al 12: 0f 85 45 01 00 00 jne 0x15d 18: 45 89 38 mov %r15d,(%r8) 1b: 4f 8d 3c d6 lea (%r14,%r10,8),%r15 1f: 4c 89 f8 mov %r15,%rax 22: 48 c1 e8 03 shr $0x3,%rax 26: 80 3c 10 00 cmpb $0x0,(%rax,%rdx,1) * 2a: 74 1e je 0x4a <-- trapping instruction 2c: 4c 89 ff mov %r15,%rdi 2f: 49 89 d6 mov %rdx,%r14 32: 4d 89 c4 mov %r8,%r12 35: 4c 89 cb mov %r9,%rbx 38: e8 55 9b 4a 00 call 0x4a9b92 3d: 49 89 d9 mov %rbx,%r9