================================================================== BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xe8/0x100 net/l2tp/l2tp_core.c:917 Read of size 4 at addr ffff8801d4771b80 by task syzkaller653530/5400 CPU: 0 PID: 5400 Comm: syzkaller653530 Not tainted 4.9.81-gd2c57b6 #34 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 ffff8801d3907878 ffffffff81d94de9 ffffea000751dc00 ffff8801d4771b80 0000000000000000 ffff8801d4771b80 ffffffff82ed49f0 ffff8801d39078b0 ffffffff8153e173 ffff8801d4771b80 0000000000000004 0000000000000000 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x128 lib/dump_stack.c:51 [] print_address_description+0x73/0x280 mm/kasan/report.c:252 [] kasan_report_error mm/kasan/report.c:351 [inline] [] kasan_report+0x275/0x360 mm/kasan/report.c:408 [] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428 [] l2tp_session_queue_purge+0xe8/0x100 net/l2tp/l2tp_core.c:917 [] pppol2tp_release+0x1ff/0x2e0 net/l2tp/l2tp_ppp.c:492 [] sock_release+0x8d/0x1e0 net/socket.c:599 [] sock_close+0x16/0x20 net/socket.c:1046 [] __fput+0x28c/0x6e0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x115/0x190 kernel/task_work.c:116 [] exit_task_work include/linux/task_work.h:21 [inline] [] do_exit+0x7e7/0x2a40 kernel/exit.c:833 [] do_group_exit+0x108/0x320 kernel/exit.c:937 [] get_signal+0x4d4/0x14e0 kernel/signal.c:2317 [] 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 arch/x86/entry/common.c:191 [inline] [] syscall_return_slowpath arch/x86/entry/common.c:260 [inline] [] do_syscall_64+0x370/0x490 arch/x86/entry/common.c:287 [] entry_SYSCALL_64_after_swapgs+0x47/0xc5 Allocated by task 5393: 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+0xad/0xe0 mm/kasan/kasan.c:609 __kmalloc+0x11d/0x310 mm/slub.c:3741 kmalloc include/linux/slab.h:495 [inline] kzalloc include/linux/slab.h:636 [inline] l2tp_session_create+0x38/0x1770 net/l2tp/l2tp_core.c:1839 pppol2tp_connect+0x10fe/0x18f0 net/l2tp/l2tp_ppp.c:711 SYSC_connect+0x1b6/0x310 net/socket.c:1562 SyS_connect+0x24/0x30 net/socket.c:1543 do_syscall_64+0x1a5/0x490 arch/x86/entry/common.c:282 entry_SYSCALL_64_after_swapgs+0x47/0xc5 Freed by task 5390: 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+0x103/0x300 mm/slub.c:3878 l2tp_session_free+0x166/0x200 net/l2tp/l2tp_core.c:1766 l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:297 [inline] l2tp_tunnel_closeall+0x26c/0x3a0 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+0x6b/0x2f0 net/core/sock.c:2727 udp_lib_close+0x15/0x20 include/net/udp.h:203 inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:434 inet6_release+0x50/0x70 net/ipv6/af_inet6.c:440 sock_release+0x8d/0x1e0 net/socket.c:599 sock_close+0x16/0x20 net/socket.c:1046 __fput+0x28c/0x6e0 fs/file_table.c:208 ____fput+0x15/0x20 fs/file_table.c:244 task_work_run+0x115/0x190 kernel/task_work.c:116 exit_task_work include/linux/task_work.h:21 [inline] do_exit+0x7e7/0x2a40 kernel/exit.c:833 do_group_exit+0x108/0x320 kernel/exit.c:937 get_signal+0x4d4/0x14e0 kernel/signal.c:2317 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 arch/x86/entry/common.c:191 [inline] syscall_return_slowpath arch/x86/entry/common.c:260 [inline] do_syscall_64+0x370/0x490 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_swapgs+0x47/0xc5 The buggy address belongs to the object at ffff8801d4771b80 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff8801d4771b80, ffff8801d4771d80) The buggy address belongs to the page: page:ffffea000751dc00 count:1 mapcount:0 mapping: (null) index:0xffff8801d4771400 compound_mapcount: 0 flags: 0x8000000000004080(slab|head) page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8801d4771a80: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc ffff8801d4771b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff8801d4771b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8801d4771c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8801d4771c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================