================================================================== BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:917 Read of size 4 at addr ffff8801b6fdc500 by task syz-executor196/3943 CPU: 1 PID: 3943 Comm: syz-executor196 Not tainted 4.9.119-g9dc978d #27 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 ffff8801b6dff8a8 ffffffff81eb4be9 ffffea0006dbf700 ffff8801b6fdc500 0000000000000000 ffff8801b6fdc500 ffffffff83015be0 ffff8801b6dff8e0 ffffffff81567f89 ffff8801b6fdc500 0000000000000004 0000000000000000 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x128 lib/dump_stack.c:51 [] print_address_description+0x6c/0x234 mm/kasan/report.c:256 [] kasan_report_error mm/kasan/report.c:355 [inline] [] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412 [] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432 [] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:917 [] pppol2tp_release+0x1fb/0x2e0 net/l2tp/l2tp_ppp.c:492 [] sock_release+0x96/0x1c0 net/socket.c:600 [] sock_close+0x16/0x20 net/socket.c:1047 [] __fput+0x263/0x700 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x10c/0x180 kernel/task_work.c:116 [] exit_task_work include/linux/task_work.h:21 [inline] [] do_exit+0x9e1/0x27b0 kernel/exit.c:833 [] do_group_exit+0x111/0x340 kernel/exit.c:937 [] get_signal+0x4cf/0x1450 kernel/signal.c:2321 [] do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807 [] exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157 [] prepare_exit_to_usermode+0xbb/0xe0 arch/x86/entry/common.c:191 [] retint_user+0x8/0x3c Allocated by task 3940: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57 save_stack+0x43/0xd0 mm/kasan/kasan.c:505 set_track mm/kasan/kasan.c:517 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:609 __kmalloc+0x11d/0x300 mm/slub.c:3741 kmalloc include/linux/slab.h:495 [inline] kzalloc include/linux/slab.h:636 [inline] l2tp_session_create+0x38/0x16f0 net/l2tp/l2tp_core.c:1843 pppol2tp_connect+0x10d7/0x18f0 net/l2tp/l2tp_ppp.c:718 SYSC_connect+0x1b8/0x300 net/socket.c:1563 SyS_connect+0x24/0x30 net/socket.c:1544 do_syscall_32_irqs_on arch/x86/entry/common.c:325 [inline] do_fast_syscall_32+0x2f7/0x870 arch/x86/entry/common.c:387 entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137 Freed by task 3897: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57 save_stack+0x43/0xd0 mm/kasan/kasan.c:505 set_track mm/kasan/kasan.c:517 [inline] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:582 slab_free_hook mm/slub.c:1355 [inline] slab_free_freelist_hook mm/slub.c:1377 [inline] slab_free mm/slub.c:2958 [inline] kfree+0xfb/0x310 mm/slub.c:3878 l2tp_session_free+0x166/0x200 net/l2tp/l2tp_core.c:1770 l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:297 [inline] l2tp_tunnel_closeall+0x284/0x350 net/l2tp/l2tp_core.c:1373 l2tp_udp_encap_destroy+0x87/0xe0 net/l2tp/l2tp_core.c:1394 udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1336 sk_common_release+0x6d/0x300 net/core/sock.c:2727 udp_lib_close+0x15/0x20 include/net/udp.h:203 inet_release+0xff/0x1d0 net/ipv4/af_inet.c:434 inet6_release+0x50/0x70 net/ipv6/af_inet6.c:440 sock_release+0x96/0x1c0 net/socket.c:600 sock_close+0x16/0x20 net/socket.c:1047 __fput+0x263/0x700 fs/file_table.c:208 ____fput+0x15/0x20 fs/file_table.c:244 task_work_run+0x10c/0x180 kernel/task_work.c:116 exit_task_work include/linux/task_work.h:21 [inline] do_exit+0x9e1/0x27b0 kernel/exit.c:833 do_group_exit+0x111/0x340 kernel/exit.c:937 get_signal+0x4cf/0x1450 kernel/signal.c:2321 do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807 exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157 prepare_exit_to_usermode+0xbb/0xe0 arch/x86/entry/common.c:191 retint_user+0x8/0x3c The buggy address belongs to the object at ffff8801b6fdc500 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff8801b6fdc500, ffff8801b6fdc700) The buggy address belongs to the page: page:ffffea0006dbf700 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 flags: 0x8000000000004080(slab|head) page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8801b6fdc400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8801b6fdc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff8801b6fdc500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8801b6fdc580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8801b6fdc600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================