================================================================== BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xe8/0x100 net/l2tp/l2tp_core.c:830 Read of size 4 at addr ffff8801d531a500 by task syzkaller804153/5530 CPU: 1 PID: 5530 Comm: syzkaller804153 Not tainted 4.4.111-gc2f631b #27 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 0000000000000000 e127fc4aa79f354b ffff8801d07c7cc8 ffffffff81d0513d ffffea000754c680 ffff8801d531a500 0000000000000000 ffff8801d531a500 ffffffff82de9cf0 ffff8801d07c7d00 ffffffff814fd433 ffff8801d531a500 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_queue_purge+0xe8/0x100 net/l2tp/l2tp_core.c:830 [] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509 [] 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+0x145/0x170 arch/x86/entry/common.c:251 [] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347 [] int_ret_from_sys_call+0x25/0xa3 Allocated by task 5528: [] 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 [] entry_SYSCALL_64_fastpath+0x16/0x92 Freed by task 5522: [] 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+0x145/0x170 arch/x86/entry/common.c:251 [] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347 [] int_ret_from_sys_call+0x25/0xa3 The buggy address belongs to the object at ffff8801d531a500 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff8801d531a500, ffff8801d531a700) The buggy address belongs to the page: kasan: CONFIG_KASAN_INLINE enabled kasan: GPF could be caused by NULL-ptr deref or user memory access[ 35.751480] ------------[ cut here ]------------ WARNING: CPU: 0 PID: 4990 at kernel/sched/core.c:7928 __might_sleep+0x138/0x1a0 kernel/sched/core.c:7923() do not call blocking ops when !TASK_RUNNING; state=1 set at [] do_nanosleep+0x113/0x4f0 kernel/time/hrtimer.c:1491