[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 16.722390] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [ 16.963031] random: sshd: uninitialized urandom read (32 bytes read) [ 17.250025] random: sshd: uninitialized urandom read (32 bytes read) Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 17.986279] random: sshd: uninitialized urandom read (32 bytes read) [ 18.124412] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.4' (ECDSA) to the list of known hosts. [ 23.558070] random: sshd: uninitialized urandom read (32 bytes read) executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program [ 23.901395] ================================================================== [ 23.908834] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 23.916087] Read of size 4 at addr ffff8801b6fdc500 by task syz-executor196/3943 [ 23.923596] [ 23.925208] CPU: 1 PID: 3943 Comm: syz-executor196 Not tainted 4.9.119-g9dc978d #27 [ 23.932975] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 23.942341] ffff8801b6dff8a8 ffffffff81eb4be9 ffffea0006dbf700 ffff8801b6fdc500 [ 23.950359] 0000000000000000 ffff8801b6fdc500 ffffffff83015be0 ffff8801b6dff8e0 [ 23.958382] ffffffff81567f89 ffff8801b6fdc500 0000000000000004 0000000000000000 [ 23.966378] Call Trace: [ 23.968946] [] dump_stack+0xc1/0x128 [ 23.974290] [] ? sock_release+0x1c0/0x1c0 [ 23.980154] [] print_address_description+0x6c/0x234 [ 23.986812] [] ? sock_release+0x1c0/0x1c0 [ 23.992589] [] kasan_report.cold.6+0x242/0x2fe [ 23.998800] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 24.005531] [] __asan_report_load4_noabort+0x14/0x20 [ 24.012262] [] l2tp_session_queue_purge+0xf4/0x100 [ 24.018822] [] ? sock_release+0x1c0/0x1c0 [ 24.024597] [] pppol2tp_release+0x1fb/0x2e0 [ 24.030547] [] sock_release+0x96/0x1c0 [ 24.036062] [] sock_close+0x16/0x20 [ 24.041317] [] __fput+0x263/0x700 [ 24.046435] [] ____fput+0x15/0x20 [ 24.051522] [] task_work_run+0x10c/0x180 [ 24.057213] [] do_exit+0x9e1/0x27b0 [ 24.062492] [] ? __sigqueue_free.part.26+0x51/0x60 [ 24.069051] [] ? release_task.part.19+0x1210/0x1210 [ 24.075701] [] do_group_exit+0x111/0x340 [ 24.081392] [] get_signal+0x4cf/0x1450 [ 24.086905] [] do_signal+0x87/0x19f0 [ 24.092250] [] ? __lock_is_held+0xa2/0xf0 [ 24.098022] [] ? setup_sigcontext+0x7d0/0x7d0 [ 24.104145] [] ? __bad_area_nosemaphore+0x1a1/0x270 [ 24.110787] [] ? bad_area+0x53/0x80 [ 24.116040] [] ? __do_page_fault+0x183/0xd50 [ 24.122075] [] ? exit_to_usermode_loop+0xac/0x120 [ 24.128540] [] exit_to_usermode_loop+0xe1/0x120 [ 24.134837] [] prepare_exit_to_usermode+0xbb/0xe0 [ 24.141306] [] retint_user+0x8/0x3c [ 24.146555] [ 24.148161] Allocated by task 3940: [ 24.151764] save_stack_trace+0x16/0x20 [ 24.155716] save_stack+0x43/0xd0 [ 24.159146] kasan_kmalloc+0xc7/0xe0 [ 24.162839] __kmalloc+0x11d/0x300 [ 24.166358] l2tp_session_create+0x38/0x16f0 [ 24.170742] pppol2tp_connect+0x10d7/0x18f0 [ 24.175042] SYSC_connect+0x1b8/0x300 [ 24.178821] SyS_connect+0x24/0x30 [ 24.182338] do_fast_syscall_32+0x2f7/0x870 [ 24.186636] entry_SYSENTER_compat+0x90/0xa2 [ 24.191014] [ 24.192622] Freed by task 3897: [ 24.195899] save_stack_trace+0x16/0x20 [ 24.199857] save_stack+0x43/0xd0 [ 24.203289] kasan_slab_free+0x72/0xc0 [ 24.207153] kfree+0xfb/0x310 [ 24.210238] l2tp_session_free+0x166/0x200 [ 24.214451] l2tp_tunnel_closeall+0x284/0x350 [ 24.218941] l2tp_udp_encap_destroy+0x87/0xe0 [ 24.223416] udpv6_destroy_sock+0xb1/0xd0 [ 24.227543] sk_common_release+0x6d/0x300 [ 24.231667] udp_lib_close+0x15/0x20 [ 24.235361] inet_release+0xff/0x1d0 [ 24.239068] inet6_release+0x50/0x70 [ 24.242764] sock_release+0x96/0x1c0 [ 24.246455] sock_close+0x16/0x20 [ 24.249884] __fput+0x263/0x700 [ 24.253137] ____fput+0x15/0x20 [ 24.256392] task_work_run+0x10c/0x180 [ 24.260278] do_exit+0x9e1/0x27b0 [ 24.263711] do_group_exit+0x111/0x340 [ 24.267576] get_signal+0x4cf/0x1450 [ 24.271268] do_signal+0x87/0x19f0 [ 24.274784] exit_to_usermode_loop+0xe1/0x120 [ 24.279342] prepare_exit_to_usermode+0xbb/0xe0 [ 24.284024] retint_user+0x8/0x3c [ 24.287465] [ 24.289070] The buggy address belongs to the object at ffff8801b6fdc500 [ 24.289070] which belongs to the cache kmalloc-512 of size 512 [ 24.301707] The buggy address is located 0 bytes inside of [ 24.301707] 512-byte region [ffff8801b6fdc500, ffff8801b6fdc700) [ 24.313398] The buggy address belongs to the page: [ 24.318308] page:ffffea0006dbf700 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 24.328495] flags: 0x8000000000004080(slab|head) [ 24.333222] page dumped because: kasan: bad access detected [ 24.338905] [ 24.340506] Memory state around the buggy address: [ 24.345409] ffff8801b6fdc400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb executing program [ 24.352745] ffff8801b6fdc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 24.360079] >ffff8801b6fdc500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.367423] ^ [ 24.370764] ffff8801b6fdc580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.378099] ffff8801b6fdc600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.385430] ================================================================== [ 24.392775] Disabling lock debugging due to kernel taint [ 24.401516] Kernel panic - not syncing: panic_on_warn set ... [ 24.401516] [ 24.408887] CPU: 1 PID: 3943 Comm: syz-executor196 Tainted: G B 4.9.119-g9dc978d #27 [ 24.417871] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 24.427209] ffff8801b6dff808 ffffffff81eb4be9 ffffffff843c893f 00000000ffffffff [ 24.435228] 0000000000000000 0000000000000001 ffffffff83015be0 ffff8801b6dff8c8 [ 24.443220] ffffffff81421c95 0000000041b58ab3 ffffffff843bc020 ffffffff81421ad6 [ 24.451250] Call Trace: [ 24.453819] [] dump_stack+0xc1/0x128 [ 24.459162] [] ? sock_release+0x1c0/0x1c0 [ 24.464938] [] panic+0x1bf/0x3bc [ 24.469952] [] ? add_taint.cold.6+0x16/0x16 [ 24.475928] [] ? ___preempt_schedule+0x16/0x18 [ 24.482138] [] kasan_end_report+0x47/0x4f [ 24.487909] [] kasan_report.cold.6+0x76/0x2fe [ 24.494040] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 24.500813] [] __asan_report_load4_noabort+0x14/0x20 [ 24.507544] [] l2tp_session_queue_purge+0xf4/0x100 [ 24.514118] [] ? sock_release+0x1c0/0x1c0 [ 24.519915] [] pppol2tp_release+0x1fb/0x2e0 [ 24.525880] [] sock_release+0x96/0x1c0 [ 24.531397] [] sock_close+0x16/0x20 [ 24.536651] [] __fput+0x263/0x700 [ 24.541751] [] ____fput+0x15/0x20 [ 24.546833] [] task_work_run+0x10c/0x180 [ 24.552522] [] do_exit+0x9e1/0x27b0 [ 24.557778] [] ? __sigqueue_free.part.26+0x51/0x60 [ 24.564333] [] ? release_task.part.19+0x1210/0x1210 [ 24.570975] [] do_group_exit+0x111/0x340 [ 24.576678] [] get_signal+0x4cf/0x1450 [ 24.582208] [] do_signal+0x87/0x19f0 [ 24.587551] [] ? __lock_is_held+0xa2/0xf0 [ 24.593344] [] ? setup_sigcontext+0x7d0/0x7d0 [ 24.599472] [] ? __bad_area_nosemaphore+0x1a1/0x270 [ 24.606127] [] ? bad_area+0x53/0x80 [ 24.611381] [] ? __do_page_fault+0x183/0xd50 [ 24.617413] [] ? exit_to_usermode_loop+0xac/0x120 [ 24.623883] [] exit_to_usermode_loop+0xe1/0x120 [ 24.630189] [] prepare_exit_to_usermode+0xbb/0xe0 [ 24.636699] [] retint_user+0x8/0x3c [ 24.642326] Dumping ftrace buffer: [ 24.645852] (ftrace buffer empty) [ 24.649539] Kernel Offset: disabled [ 24.653142] Rebooting in 86400 seconds..