audit: type=1400 audit(1521051925.126:21): avc: denied { read } for pid=6657 comm="syz-executor0" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1 ================================================================== BUG: KASAN: use-after-free in l2tp_session_create+0xf94/0x10f0 net/l2tp/l2tp_core.c:1824 Read of size 4 at addr ffff8801d7505910 by task syz-executor7/6672 CPU: 1 PID: 6672 Comm: syz-executor7 Not tainted 4.4.120-gd63fdf6 #29 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 0000000000000000 c701a29bcde8a356 ffff8800b9f2fa30 ffffffff81d0408d ffffea00075d4100 ffff8801d7505910 0000000000000000 ffff8801d7505910 ffff8801d7505900 ffff8800b9f2fa68 ffffffff814fe143 ffff8801d7505910 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x124 lib/dump_stack.c:51 [] print_address_description+0x73/0x260 mm/kasan/report.c:252 [] kasan_report_error mm/kasan/report.c:351 [inline] [] kasan_report+0x285/0x370 mm/kasan/report.c:408 [] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428 [] l2tp_session_create+0xf94/0x10f0 net/l2tp/l2tp_core.c:1824 [] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718 [] SYSC_connect+0x1b6/0x310 net/socket.c:1557 [] SyS_connect+0x24/0x30 net/socket.c:1538 [] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline] [] do_fast_syscall_32+0x321/0x8a0 arch/x86/entry/common.c:459 [] sysenter_flags_fixed+0xd/0x17 Allocated by task 6672: [] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63 [] save_stack+0x43/0xd0 mm/kasan/kasan.c:512 [] set_track mm/kasan/kasan.c:524 [inline] [] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616 [] __kmalloc+0x124/0x320 mm/slub.c:3613 [] kmalloc include/linux/slab.h:481 [inline] [] kzalloc include/linux/slab.h:620 [inline] [] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744 [] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718 [] SYSC_connect+0x1b6/0x310 net/socket.c:1557 [] SyS_connect+0x24/0x30 net/socket.c:1538 [] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline] [] do_fast_syscall_32+0x321/0x8a0 arch/x86/entry/common.c:459 [] sysenter_flags_fixed+0xd/0x17 Freed by task 6675: [] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63 [] save_stack+0x43/0xd0 mm/kasan/kasan.c:512 [] set_track mm/kasan/kasan.c:524 [inline] [] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589 [] slab_free_hook mm/slub.c:1383 [inline] [] slab_free_freelist_hook mm/slub.c:1405 [inline] [] slab_free mm/slub.c:2859 [inline] [] kfree+0xfc/0x300 mm/slub.c:3749 [] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672 [] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline] [] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279 [] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300 [] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421 [] sk_common_release+0x6b/0x300 net/core/sock.c:2680 [] udp_lib_close+0x15/0x20 include/net/udp.h:190 [] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435 [] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424 [] sock_release+0x8d/0x1e0 net/socket.c:586 [] sock_close+0x16/0x20 net/socket.c:1037 [] __fput+0x233/0x6d0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x104/0x180 kernel/task_work.c:115 [] tracehook_notify_resume include/linux/tracehook.h:191 [inline] [] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:252 [] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline] [] syscall_return_slowpath arch/x86/entry/common.c:348 [inline] [] do_syscall_32_irqs_on arch/x86/entry/common.c:398 [inline] [] do_fast_syscall_32+0x614/0x8a0 arch/x86/entry/common.c:459 [] sysenter_flags_fixed+0xd/0x17 The buggy address belongs to the object at ffff8801d7505900 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 16 bytes inside of 512-byte region [ffff8801d7505900, ffff8801d7505b00) The buggy address belongs to the page: BUG: unable to handle kernel NULL pointer dereference at (null) IP: [< (null)>] (null) PGD 80000001cf3e1067 PUD 1ce0ed067 PMD 0 kasan: CONFIG_KASAN_INLINE enabled kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 0 PID: 0 Comm: Not tainted 4.4.120-gd63fdf6 #29 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8800b94c6000 task.stack: (null) RIP: 0010:[] [] no_context+0x27b/0x840 arch/x86/mm/fault.c:721 RSP: 0018:ffff8800b96d7278 EFLAGS: 00010006 RAX: dffffc0000000000 RBX: 1ffff100172dae54 RCX: ffffffff810db551 RDX: 0000000000000005 RSI: ffffffff839fe520 RDI: 0000000000000028 RBP: ffff8800b96d7328 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 1ffff100172dadc2 R12: 0000000000000000 R13: ffff8800b96d7458 R14: 0000000000000000 R15: ffff8800b94c6000 FS: 0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f6f8eb40 CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 CR2: 0000000000000000 CR3: 00000001cccbc000 CR4: 0000000000160670 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: ffffffff838a9060 0000000000000046 ffff8801cccbc000 0000000000000000 0000000000000010 0000000041b58ab3 ffffffff83fa7bf0 ffffffff810db310 ffffffff838a9060 0000000000000003 0000000000000000 ffff8800b96d7310 Call Trace: Code: 89 fa 48 c1 ea 03 80 3c 02 00 74 05 e8 2f 32 42 00 48 b8 00 00 00 00 00 fc ff df 4d 8b 67 08 49 8d 7c 24 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 74 05 e8 0a 32 42 00 49 81 7c 24 28 9d 6e ac 57 74 RIP [] no_context+0x27b/0x840 arch/x86/mm/fault.c:721 RSP ---[ end trace 21bb2196e1c213e6 ]---