[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 14.308928] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 15.711169] random: sshd: uninitialized urandom read (32 bytes read) [ 15.879497] random: sshd: uninitialized urandom read (32 bytes read) [ 16.872615] random: sshd: uninitialized urandom read (32 bytes read) [ 34.257252] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.41' (ECDSA) to the list of known hosts. [ 39.755680] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 39.896587] ================================================================== [ 39.903967] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 39.911227] Read of size 4 at addr ffff8801cb6d1b80 by task syz-executor966/3734 [ 39.918729] [ 39.920330] CPU: 0 PID: 3734 Comm: syz-executor966 Not tainted 4.9.109-ga4230be #51 [ 39.928180] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 39.937515] ffff8801bddbfcb0 ffffffff81eb3e29 ffffea00072db400 ffff8801cb6d1b80 [ 39.945503] 0000000000000000 ffff8801cb6d1b80 ffffffff83013be0 ffff8801bddbfce8 [ 39.953494] ffffffff81567a89 ffff8801cb6d1b80 0000000000000004 0000000000000000 [ 39.961478] Call Trace: [ 39.964052] [] dump_stack+0xc1/0x128 [ 39.969394] [] ? sock_release+0x1c0/0x1c0 [ 39.975163] [] print_address_description+0x6c/0x234 [ 39.981810] [] ? sock_release+0x1c0/0x1c0 [ 39.987580] [] kasan_report.cold.6+0x242/0x2fe [ 39.993785] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 40.000508] [] __asan_report_load4_noabort+0x14/0x20 [ 40.007228] [] l2tp_session_queue_purge+0xf4/0x100 [ 40.013789] [] ? sock_release+0x1c0/0x1c0 [ 40.019554] [] pppol2tp_release+0x1fb/0x2e0 [ 40.025506] [] sock_release+0x96/0x1c0 [ 40.031023] [] sock_close+0x16/0x20 [ 40.036273] [] __fput+0x263/0x700 [ 40.041347] [] ____fput+0x15/0x20 [ 40.046427] [] task_work_run+0x10c/0x180 [ 40.052115] [] exit_to_usermode_loop+0xfc/0x120 [ 40.058411] [] do_syscall_64+0x364/0x490 [ 40.064096] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 40.070994] [ 40.072597] Allocated by task 3733: [ 40.076201] save_stack_trace+0x16/0x20 [ 40.080166] save_stack+0x43/0xd0 [ 40.083589] kasan_kmalloc+0xc7/0xe0 [ 40.087275] __kmalloc+0x11d/0x300 [ 40.090790] l2tp_session_create+0x38/0x16f0 [ 40.095169] pppol2tp_connect+0x10d7/0x18f0 [ 40.099462] SYSC_connect+0x1b8/0x300 [ 40.103233] SyS_connect+0x24/0x30 [ 40.106744] do_syscall_64+0x1a6/0x490 [ 40.110605] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 40.115675] [ 40.117276] Freed by task 3733: [ 40.120531] save_stack_trace+0x16/0x20 [ 40.124476] save_stack+0x43/0xd0 [ 40.127899] kasan_slab_free+0x72/0xc0 [ 40.131758] kfree+0xfb/0x310 [ 40.134836] l2tp_session_free+0x166/0x200 [ 40.139053] l2tp_tunnel_closeall+0x284/0x350 [ 40.143522] l2tp_udp_encap_destroy+0x87/0xe0 [ 40.147993] udp_destroy_sock+0x118/0x1a0 [ 40.152117] sk_common_release+0x6d/0x300 [ 40.156234] udp_lib_close+0x15/0x20 [ 40.159928] inet_release+0xff/0x1d0 [ 40.163611] sock_release+0x96/0x1c0 [ 40.167293] sock_close+0x16/0x20 [ 40.170719] __fput+0x263/0x700 [ 40.173971] ____fput+0x15/0x20 [ 40.177229] task_work_run+0x10c/0x180 [ 40.181090] exit_to_usermode_loop+0xfc/0x120 [ 40.185554] do_syscall_64+0x364/0x490 [ 40.189414] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 40.194485] [ 40.196086] The buggy address belongs to the object at ffff8801cb6d1b80 [ 40.196086] which belongs to the cache kmalloc-512 of size 512 [ 40.208714] The buggy address is located 0 bytes inside of [ 40.208714] 512-byte region [ffff8801cb6d1b80, ffff8801cb6d1d80) [ 40.220387] The buggy address belongs to the page: [ 40.225289] page:ffffea00072db400 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 40.235466] flags: 0x8000000000004080(slab|head) [ 40.240190] page dumped because: kasan: bad access detected [ 40.245868] [ 40.247465] Memory state around the buggy address: [ 40.252366] ffff8801cb6d1a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 40.259694] ffff8801cb6d1b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 40.267032] >ffff8801cb6d1b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 40.274358] ^ [ 40.277693] ffff8801cb6d1c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 40.285021] ffff8801cb6d1c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 40.292350] ================================================================== [ 40.299677] Disabling lock debugging due to kernel taint [ 40.305381] Kernel panic - not syncing: panic_on_warn set ... [ 40.305381] [ 40.312726] CPU: 0 PID: 3734 Comm: syz-executor966 Tainted: G B 4.9.109-ga4230be #51 [ 40.321709] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 40.331046] ffff8801bddbfc10 ffffffff81eb3e29 ffffffff843c6327 00000000ffffffff [ 40.339024] 0000000000000000 0000000000000000 ffffffff83013be0 ffff8801bddbfcd0 [ 40.346998] ffffffff81421925 0000000041b58ab3 ffffffff843b9a40 ffffffff81421766 [ 40.354985] Call Trace: [ 40.357547] [] dump_stack+0xc1/0x128 [ 40.362895] [] ? sock_release+0x1c0/0x1c0 [ 40.369098] [] panic+0x1bf/0x3bc [ 40.374088] [] ? add_taint.cold.6+0x16/0x16 [ 40.380031] [] ? ___preempt_schedule+0x16/0x18 [ 40.386245] [] kasan_end_report+0x47/0x4f [ 40.392011] [] kasan_report.cold.6+0x76/0x2fe [ 40.398127] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 40.404851] [] __asan_report_load4_noabort+0x14/0x20 [ 40.411581] [] l2tp_session_queue_purge+0xf4/0x100 [ 40.418131] [] ? sock_release+0x1c0/0x1c0 [ 40.423901] [] pppol2tp_release+0x1fb/0x2e0 [ 40.429844] [] sock_release+0x96/0x1c0 [ 40.435359] [] sock_close+0x16/0x20 [ 40.440609] [] __fput+0x263/0x700 [ 40.445691] [] ____fput+0x15/0x20 [ 40.450779] [] task_work_run+0x10c/0x180 [ 40.456461] [] exit_to_usermode_loop+0xfc/0x120 [ 40.462750] [] do_syscall_64+0x364/0x490 [ 40.468434] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 40.475753] Dumping ftrace buffer: [ 40.479274] (ftrace buffer empty) [ 40.482959] Kernel Offset: disabled [ 40.486558] Rebooting in 86400 seconds..