bisecting fixing commit since e132c8d7b58d8dc2c1888f5768454550d1f3ea7b building syzkaller on b5268b89c2964733654c89f8322fb155d9fa6799 testing commit e132c8d7b58d8dc2c1888f5768454550d1f3ea7b with gcc (GCC) 8.1.0 kernel signature: 6753f7e31175bf4c15c5d5959770ef13b28a6a35d6a7fc48f0e445bddc2fd453 run #0: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #1: crashed: KASAN: use-after-free Read in l2tp_session_create run #2: crashed: KASAN: use-after-free Read in lock_sock_nested run #3: crashed: KASAN: use-after-free Read in lock_sock_nested run #4: crashed: KASAN: use-after-free Read in l2tp_session_create run #5: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #6: crashed: KASAN: use-after-free Read in lock_sock_nested run #7: crashed: KASAN: use-after-free Read in l2tp_session_create run #8: crashed: KASAN: use-after-free Read in l2tp_session_create run #9: crashed: KASAN: use-after-free Read in pppol2tp_session_close testing current HEAD 12cd844a39ed16aa183a820a54fe6f9a0bb4cd14 testing commit 12cd844a39ed16aa183a820a54fe6f9a0bb4cd14 with gcc (GCC) 8.1.0 kernel signature: 59964dc6cb90068b6939f39c020f2527c104540556a6790257f76041a47a9517 run #0: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #1: crashed: KASAN: use-after-free Read in pppol2tp_connect run #2: crashed: KASAN: use-after-free Read in pppol2tp_release run #3: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #4: crashed: KASAN: use-after-free Read in l2tp_session_create run #5: crashed: KASAN: use-after-free Read in l2tp_session_create run #6: crashed: KASAN: use-after-free Write in pppol2tp_connect run #7: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #8: crashed: KASAN: use-after-free Read in l2tp_session_create run #9: crashed: KASAN: use-after-free Read in l2tp_session_create revisions tested: 2, total time: 24m47.059004219s (build: 16m33.553453721s, test: 7m1.000232842s) the crash still happens on HEAD commit msg: Linux 4.14.173 crash: KASAN: use-after-free Read in l2tp_session_create l2tp_core: tunl 4: sockfd_lookup(fd=4) returned -9 l2tp_core: tunl 4: sockfd_lookup(fd=4) returned -9 l2tp_core: tunl 4: sockfd_lookup(fd=4) returned -9 l2tp_core: tunl 4: sockfd_lookup(fd=4) returned -9 ================================================================== BUG: KASAN: use-after-free in l2tp_session_create+0x144f/0x1720 net/l2tp/l2tp_core.c:1859 Read of size 4 at addr ffff88808d3d4a18 by task syz-executor.5/12244 CPU: 1 PID: 12244 Comm: syz-executor.5 Not tainted 4.14.173-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0xf7/0x13b lib/dump_stack.c:58 print_address_description.cold.7+0x9/0x1c9 mm/kasan/report.c:252 kasan_report_error mm/kasan/report.c:351 [inline] kasan_report.cold.8+0x11a/0x2d3 mm/kasan/report.c:409 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429 l2tp_session_create+0x144f/0x1720 net/l2tp/l2tp_core.c:1859 pppol2tp_connect+0x10c1/0x1900 net/l2tp/l2tp_ppp.c:721 SYSC_connect+0x1e3/0x2a0 net/socket.c:1655 SyS_connect+0x9/0x10 net/socket.c:1636 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x459a59 RSP: 002b:00007f1de98a7c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a59 RDX: 0000000000000026 RSI: 0000000020000180 RDI: 0000000000000005 RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1de98a86d4 R13: 00000000004c0006 R14: 00000000004d2298 R15: 00000000ffffffff Allocated by task 12244: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack+0x43/0xd0 mm/kasan/kasan.c:447 set_track mm/kasan/kasan.c:459 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:551 __do_kmalloc mm/slab.c:3720 [inline] __kmalloc+0x15b/0x7b0 mm/slab.c:3729 kmalloc include/linux/slab.h:493 [inline] kzalloc include/linux/slab.h:661 [inline] l2tp_session_create+0x34/0x1720 net/l2tp/l2tp_core.c:1796 pppol2tp_connect+0x10c1/0x1900 net/l2tp/l2tp_ppp.c:721 SYSC_connect+0x1e3/0x2a0 net/socket.c:1655 SyS_connect+0x9/0x10 net/socket.c:1636 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7 Freed by task 12249: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack+0x43/0xd0 mm/kasan/kasan.c:447 set_track mm/kasan/kasan.c:459 [inline] kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524 __cache_free mm/slab.c:3496 [inline] kfree+0xcc/0x270 mm/slab.c:3815 l2tp_session_free+0x14f/0x1d0 net/l2tp/l2tp_core.c:1719 l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:300 [inline] l2tp_tunnel_closeall+0x23d/0x2f0 net/l2tp/l2tp_core.c:1350 l2tp_udp_encap_destroy+0x7d/0xc0 net/l2tp/l2tp_core.c:1371 udpv6_destroy_sock+0x89/0xb0 net/ipv6/udp.c:1444 sk_common_release+0x5e/0x2c0 net/core/sock.c:2989 udp_lib_close+0x9/0x10 include/net/udp.h:203 inet_release+0xd9/0x1c0 net/ipv4/af_inet.c:425 inet6_release+0x46/0x60 net/ipv6/af_inet6.c:450 __sock_release+0xc2/0x2a0 net/socket.c:602 sock_close+0x10/0x20 net/socket.c:1139 __fput+0x232/0x750 fs/file_table.c:210 ____fput+0x9/0x10 fs/file_table.c:244 task_work_run+0xe5/0x170 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:191 [inline] exit_to_usermode_loop+0x16a/0x1b0 arch/x86/entry/common.c:164 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline] syscall_return_slowpath arch/x86/entry/common.c:270 [inline] do_syscall_64+0x416/0x5b0 arch/x86/entry/common.c:297 entry_SYSCALL_64_after_hwframe+0x42/0xb7 The buggy address belongs to the object at ffff88808d3d4a00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 24 bytes inside of 512-byte region [ffff88808d3d4a00, ffff88808d3d4c00) The buggy address belongs to the page: page:ffffea000234f500 count:1 mapcount:0 mapping:ffff88808d3d4000 index:0xffff88808d3d4000 flags: 0x1fffc0000000100(slab) raw: 01fffc0000000100 ffff88808d3d4000 ffff88808d3d4000 0000000100000004 raw: ffffea00023a9a60 ffffea00023b78a0 ffff8880aa800940 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88808d3d4900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88808d3d4980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff88808d3d4a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88808d3d4a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88808d3d4b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================