bisecting fixing commit since e1f7d50ae3a3ec342e87a9b1ce6787bfb8b3c08b building syzkaller on af6b8ef8f18c45343685f0ee7af9dd3a4b2b5d95 testing commit e1f7d50ae3a3ec342e87a9b1ce6787bfb8b3c08b with gcc (GCC) 8.1.0 kernel signature: 854c7dad0ea598a1fad2e77c4edbe7a4e9844be3d71d0ae8aa20bad5c7ed5eec all runs: crashed: KASAN: use-after-free Read in pppol2tp_session_close testing current HEAD 98db2bf27b9ed2d5ed0b6c9c8a4bfcb127a19796 testing commit 98db2bf27b9ed2d5ed0b6c9c8a4bfcb127a19796 with gcc (GCC) 8.1.0 kernel signature: 6be05005304dfc5c783fd0e9e5d5431f4766acef9a51b5500d41af76b29961f0 run #0: crashed: KASAN: use-after-free Read in lock_sock_nested run #1: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #2: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #3: crashed: KASAN: use-after-free Write in ex_handler_refcount run #4: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #5: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #6: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #7: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #8: crashed: KASAN: use-after-free Read in pppol2tp_session_close run #9: crashed: KASAN: use-after-free Read in pppol2tp_session_close revisions tested: 2, total time: 30m17.070534608s (build: 17m57.209041944s, test: 11m33.674612835s) the crash still happens on HEAD commit msg: Linux 4.14.171 crash: KASAN: use-after-free Read in pppol2tp_session_close l2tp_core: tunl 4: sockfd_lookup(fd=3) returned -9 l2tp_core: tunl 4: sockfd_lookup(fd=4) returned -9 ================================================================== BUG: KASAN: use-after-free in inet_shutdown+0x287/0x300 net/ipv4/af_inet.c:816 Read of size 4 at addr ffff8880800dd5c0 by task syz-executor.3/17019 CPU: 1 PID: 17019 Comm: syz-executor.3 Not tainted 4.14.171-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 inet_shutdown+0x287/0x300 net/ipv4/af_inet.c:816 pppol2tp_session_close+0x91/0xc0 net/l2tp/l2tp_ppp.c:441 l2tp_tunnel_closeall+0x1df/0x2f0 net/l2tp/l2tp_core.c:1345 l2tp_udp_encap_destroy+0x79/0xb0 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 RIP: 0033:0x4144b1 RSP: 002b:00007ffc0a9cf0f0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003 RAX: 0000000000000000 RBX: 0000000000000005 RCX: 00000000004144b1 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000004 RBP: 0000000000000000 R08: ffffffffffffffff R09: ffffffffffffffff R10: 00007ffc0a9cf1d0 R11: 0000000000000293 R12: 000000000075bfc8 R13: 0000000000032599 R14: 0000000000760858 R15: 000000000075bfd4 Allocated by task 17048: 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 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489 kmem_cache_alloc+0x12e/0x790 mm/slab.c:3552 sock_alloc_inode+0x18/0x230 net/socket.c:251 alloc_inode+0x56/0x150 fs/inode.c:209 new_inode_pseudo+0xc/0xd0 fs/inode.c:898 sock_alloc+0x3c/0x280 net/socket.c:569 __sock_create+0x7a/0x540 net/socket.c:1239 sock_create net/socket.c:1315 [inline] SYSC_socket net/socket.c:1345 [inline] SyS_socket+0xc6/0x1a0 net/socket.c:1325 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7 Freed by task 17026: 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] kmem_cache_free+0x80/0x2d0 mm/slab.c:3758 sock_destroy_inode+0x50/0x60 net/socket.c:281 destroy_inode+0xb3/0x100 fs/inode.c:266 evict+0x36f/0x590 fs/inode.c:571 iput_final fs/inode.c:1523 [inline] iput+0x3ac/0x810 fs/inode.c:1550 dentry_unlink_inode+0x23e/0x2f0 fs/dcache.c:387 __dentry_kill+0x2d2/0x540 fs/dcache.c:591 dentry_kill fs/dcache.c:632 [inline] dput.part.27+0x49a/0x610 fs/dcache.c:847 dput+0xe/0x20 fs/dcache.c:810 __fput+0x3f7/0x750 fs/file_table.c:228 ____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 ffff8880800dd5c0 which belongs to the cache sock_inode_cache of size 992 The buggy address is located 0 bytes inside of 992-byte region [ffff8880800dd5c0, ffff8880800dd9a0) The buggy address belongs to the page: page:ffffea0002003740 count:1 mapcount:0 mapping:ffff8880800dd140 index:0xffff8880800ddffd flags: 0xfffe0000000100(slab) raw: 00fffe0000000100 ffff8880800dd140 ffff8880800ddffd 0000000100000003 raw: ffffea0002589de0 ffffea0002588820 ffff88821b7d2240 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880800dd480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880800dd500: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc >ffff8880800dd580: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb ^ ffff8880800dd600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880800dd680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================