[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 12.295380] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 29.333908] random: sshd: uninitialized urandom read (32 bytes read) [ 29.564745] random: sshd: uninitialized urandom read (32 bytes read) [ 30.089881] random: sshd: uninitialized urandom read (32 bytes read) [ 38.761918] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.9' (ECDSA) to the list of known hosts. [ 44.276931] 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 [ 44.979149] ================================================================== [ 44.986714] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 44.993990] Read of size 4 at addr ffff8801c82a3400 by task syz-executor381/3918 [ 45.001507] [ 45.003126] CPU: 0 PID: 3918 Comm: syz-executor381 Not tainted 4.9.119-g9dc978d #75 [ 45.010901] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 45.020244] ffff8801d966f8a8 ffffffff81eb4be9 ffffea000720a880 ffff8801c82a3400 [ 45.028245] 0000000000000000 ffff8801c82a3400 ffffffff83015be0 ffff8801d966f8e0 [ 45.036238] ffffffff81567f89 ffff8801c82a3400 0000000000000004 0000000000000000 [ 45.044242] Call Trace: [ 45.046811] [] dump_stack+0xc1/0x128 [ 45.052208] [] ? sock_release+0x1c0/0x1c0 [ 45.058001] [] print_address_description+0x6c/0x234 [ 45.064656] [] ? sock_release+0x1c0/0x1c0 [ 45.070441] [] kasan_report.cold.6+0x242/0x2fe [ 45.076664] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 45.083448] [] __asan_report_load4_noabort+0x14/0x20 [ 45.090240] [] l2tp_session_queue_purge+0xf4/0x100 [ 45.096830] [] ? sock_release+0x1c0/0x1c0 [ 45.102616] [] pppol2tp_release+0x1fb/0x2e0 [ 45.108577] [] sock_release+0x96/0x1c0 [ 45.114100] [] sock_close+0x16/0x20 [ 45.119358] [] __fput+0x263/0x700 [ 45.124444] [] ____fput+0x15/0x20 [ 45.129537] [] task_work_run+0x10c/0x180 [ 45.135233] [] do_exit+0x9e1/0x27b0 [ 45.140498] [] ? __sigqueue_free.part.26+0x51/0x60 [ 45.147061] [] ? release_task.part.19+0x1210/0x1210 [ 45.153763] [] do_group_exit+0x111/0x340 [ 45.159515] [] get_signal+0x4cf/0x1450 [ 45.165040] [] ? signal_setup_done+0xbc/0x280 [ 45.171170] [] do_signal+0x87/0x19f0 [ 45.176520] [] ? setup_sigcontext+0x7d0/0x7d0 [ 45.182655] [] ? bad_area+0x53/0x80 [ 45.187918] [] ? __do_page_fault+0x183/0xd50 [ 45.193958] [] ? exit_to_usermode_loop+0xac/0x120 [ 45.200432] [] exit_to_usermode_loop+0xe1/0x120 [ 45.206777] [] prepare_exit_to_usermode+0xbb/0xe0 [ 45.213256] [] retint_user+0x8/0x3c [ 45.218557] [ 45.220168] Allocated by task 3915: [ 45.223772] save_stack_trace+0x16/0x20 [ 45.227721] save_stack+0x43/0xd0 [ 45.231153] kasan_kmalloc+0xc7/0xe0 [ 45.234843] __kmalloc+0x11d/0x300 [ 45.238358] l2tp_session_create+0x38/0x16f0 [ 45.242742] pppol2tp_connect+0x10d7/0x18f0 [ 45.247041] SYSC_connect+0x1b8/0x300 [ 45.250823] SyS_connect+0x24/0x30 [ 45.254344] do_syscall_64+0x1a6/0x490 [ 45.258206] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 45.263282] [ 45.264889] Freed by task 3888: [ 45.268146] save_stack_trace+0x16/0x20 [ 45.272098] save_stack+0x43/0xd0 [ 45.275601] kasan_slab_free+0x72/0xc0 [ 45.279474] kfree+0xfb/0x310 [ 45.282554] l2tp_session_free+0x166/0x200 [ 45.286762] l2tp_tunnel_closeall+0x284/0x350 [ 45.291232] l2tp_udp_encap_destroy+0x87/0xe0 [ 45.295702] udpv6_destroy_sock+0xb1/0xd0 [ 45.299883] sk_common_release+0x6d/0x300 [ 45.304025] udp_lib_close+0x15/0x20 [ 45.307715] inet_release+0xff/0x1d0 [ 45.311405] inet6_release+0x50/0x70 [ 45.315101] sock_release+0x96/0x1c0 [ 45.318791] sock_close+0x16/0x20 [ 45.322372] __fput+0x263/0x700 [ 45.325682] ____fput+0x15/0x20 [ 45.328965] task_work_run+0x10c/0x180 [ 45.332836] do_exit+0x9e1/0x27b0 [ 45.336265] do_group_exit+0x111/0x340 [ 45.340159] get_signal+0x4cf/0x1450 [ 45.343851] do_signal+0x87/0x19f0 [ 45.347369] exit_to_usermode_loop+0xe1/0x120 [ 45.351850] prepare_exit_to_usermode+0xbb/0xe0 [ 45.356500] retint_user+0x8/0x3c [ 45.359925] [ 45.361532] The buggy address belongs to the object at ffff8801c82a3400 [ 45.361532] which belongs to the cache kmalloc-512 of size 512 [ 45.374227] The buggy address is located 0 bytes inside of [ 45.374227] 512-byte region [ffff8801c82a3400, ffff8801c82a3600) [ 45.385915] The buggy address belongs to the page: [ 45.390831] page:ffffea000720a880 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 45.401126] flags: 0x8000000000004080(slab|head) [ 45.405855] page dumped because: kasan: bad access detected [ 45.411539] [ 45.413148] Memory state around the buggy address: [ 45.418053] ffff8801c82a3300: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc [ 45.425394] ffff8801c82a3380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 45.432735] >ffff8801c82a3400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 45.440079] ^ [ 45.443425] ffff8801c82a3480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 45.450764] ffff8801c82a3500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 45.458103] ================================================================== [ 45.465437] Disabling lock debugging due to kernel taint [ 45.471871] Kernel panic - not syncing: panic_on_warn set ... [ 45.471871] [ 45.479246] CPU: 0 PID: 3918 Comm: syz-executor381 Tainted: G B 4.9.119-g9dc978d #75 [ 45.488241] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 45.497585] ffff8801d966f808 ffffffff81eb4be9 ffffffff843c893f 00000000ffffffff [ 45.505601] 0000000000000000 0000000000000000 ffffffff83015be0 ffff8801d966f8c8 [ 45.513650] ffffffff81421c95 0000000041b58ab3 ffffffff843bc020 ffffffff81421ad6 [ 45.521704] Call Trace: [ 45.524269] [] dump_stack+0xc1/0x128 [ 45.529615] [] ? sock_release+0x1c0/0x1c0 [ 45.535464] [] panic+0x1bf/0x3bc [ 45.540469] [] ? add_taint.cold.6+0x16/0x16 [ 45.546420] [] ? ___preempt_schedule+0x16/0x18 [ 45.552631] [] kasan_end_report+0x47/0x4f [ 45.558418] [] kasan_report.cold.6+0x76/0x2fe [ 45.564545] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 45.571276] [] __asan_report_load4_noabort+0x14/0x20 [ 45.578009] [] l2tp_session_queue_purge+0xf4/0x100 [ 45.584567] [] ? sock_release+0x1c0/0x1c0 [ 45.590340] [] pppol2tp_release+0x1fb/0x2e0 [ 45.596287] [] sock_release+0x96/0x1c0 [ 45.601877] [] sock_close+0x16/0x20 [ 45.607141] [] __fput+0x263/0x700 [ 45.612230] [] ____fput+0x15/0x20 [ 45.617308] [] task_work_run+0x10c/0x180 [ 45.622999] [] do_exit+0x9e1/0x27b0 [ 45.628251] [] ? __sigqueue_free.part.26+0x51/0x60 [ 45.634818] [] ? release_task.part.19+0x1210/0x1210 [ 45.641525] [] do_group_exit+0x111/0x340 [ 45.647269] [] get_signal+0x4cf/0x1450 [ 45.652792] [] ? signal_setup_done+0xbc/0x280 [ 45.658928] [] do_signal+0x87/0x19f0 [ 45.664290] [] ? setup_sigcontext+0x7d0/0x7d0 [ 45.670418] [] ? bad_area+0x53/0x80 [ 45.675676] [] ? __do_page_fault+0x183/0xd50 [ 45.681711] [] ? exit_to_usermode_loop+0xac/0x120 [ 45.688185] [] exit_to_usermode_loop+0xe1/0x120 [ 45.694484] [] prepare_exit_to_usermode+0xbb/0xe0 [ 45.700957] [] retint_user+0x8/0x3c [ 45.706589] Dumping ftrace buffer: [ 45.710113] (ftrace buffer empty) [ 45.713800] Kernel Offset: disabled [ 45.717401] Rebooting in 86400 seconds..