[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 15.896881] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 17.905488] random: sshd: uninitialized urandom read (32 bytes read) [ 18.160600] random: sshd: uninitialized urandom read (32 bytes read) [ 18.998658] random: sshd: uninitialized urandom read (32 bytes read) [ 19.131771] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.37' (ECDSA) to the list of known hosts. [ 24.676765] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 24.820574] ================================================================== [ 24.827968] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 24.835214] Read of size 4 at addr ffff8801c8170f00 by task syz-executor676/3791 [ 24.842719] [ 24.844337] CPU: 1 PID: 3791 Comm: syz-executor676 Not tainted 4.9.110-g00a0bcb #56 [ 24.852114] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 24.861456] ffff8801d9657cb0 ffffffff81eb2329 ffffea0007205c00 ffff8801c8170f00 [ 24.869466] 0000000000000000 ffff8801c8170f00 ffffffff83011be0 ffff8801d9657ce8 [ 24.877471] ffffffff81567a89 ffff8801c8170f00 0000000000000004 0000000000000000 [ 24.885473] Call Trace: [ 24.888053] [] dump_stack+0xc1/0x128 [ 24.893413] [] ? sock_release+0x1c0/0x1c0 [ 24.899193] [] print_address_description+0x6c/0x234 [ 24.905853] [] ? sock_release+0x1c0/0x1c0 [ 24.911638] [] kasan_report.cold.6+0x242/0x2fe [ 24.917855] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 24.924610] [] __asan_report_load4_noabort+0x14/0x20 [ 24.931335] [] l2tp_session_queue_purge+0xf4/0x100 [ 24.937886] [] ? sock_release+0x1c0/0x1c0 [ 24.943663] [] pppol2tp_release+0x1fb/0x2e0 [ 24.949611] [] sock_release+0x96/0x1c0 [ 24.955135] [] sock_close+0x16/0x20 [ 24.960387] [] __fput+0x263/0x700 [ 24.965472] [] ____fput+0x15/0x20 [ 24.970549] [] task_work_run+0x10c/0x180 [ 24.976235] [] exit_to_usermode_loop+0xfc/0x120 [ 24.982526] [] do_syscall_64+0x364/0x490 [ 24.988219] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 24.995116] [ 24.996736] Allocated by task 3789: [ 25.000347] save_stack_trace+0x16/0x20 [ 25.004312] save_stack+0x43/0xd0 [ 25.007744] kasan_kmalloc+0xc7/0xe0 [ 25.011435] __kmalloc+0x11d/0x300 [ 25.014957] l2tp_session_create+0x38/0x16f0 [ 25.019349] pppol2tp_connect+0x10d7/0x18f0 [ 25.023654] SYSC_connect+0x1b8/0x300 [ 25.027456] SyS_connect+0x24/0x30 [ 25.030980] do_syscall_64+0x1a6/0x490 [ 25.034851] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 25.039927] [ 25.041529] Freed by task 3789: [ 25.044788] save_stack_trace+0x16/0x20 [ 25.048746] save_stack+0x43/0xd0 [ 25.052192] kasan_slab_free+0x72/0xc0 [ 25.056050] kfree+0xfb/0x310 [ 25.059130] l2tp_session_free+0x166/0x200 [ 25.063340] l2tp_tunnel_closeall+0x284/0x350 [ 25.067822] l2tp_udp_encap_destroy+0x87/0xe0 [ 25.072288] udpv6_destroy_sock+0xb1/0xd0 [ 25.076417] sk_common_release+0x6d/0x300 [ 25.080535] udp_lib_close+0x15/0x20 [ 25.084222] inet_release+0xff/0x1d0 [ 25.087905] inet6_release+0x50/0x70 [ 25.091590] sock_release+0x96/0x1c0 [ 25.095283] sock_close+0x16/0x20 [ 25.098715] __fput+0x263/0x700 [ 25.101968] ____fput+0x15/0x20 [ 25.105223] task_work_run+0x10c/0x180 [ 25.109087] exit_to_usermode_loop+0xfc/0x120 [ 25.113560] do_syscall_64+0x364/0x490 [ 25.117428] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 25.122499] [ 25.124102] The buggy address belongs to the object at ffff8801c8170f00 [ 25.124102] which belongs to the cache kmalloc-512 of size 512 [ 25.136746] The buggy address is located 0 bytes inside of [ 25.136746] 512-byte region [ffff8801c8170f00, ffff8801c8171100) [ 25.148420] The buggy address belongs to the page: [ 25.153342] page:ffffea0007205c00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 25.163543] flags: 0x8000000000004080(slab|head) [ 25.168359] page dumped because: kasan: bad access detected [ 25.174043] [ 25.175649] Memory state around the buggy address: [ 25.180556] ffff8801c8170e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 25.187891] ffff8801c8170e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 25.195222] >ffff8801c8170f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 25.202551] ^ [ 25.205889] ffff8801c8170f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 25.213217] ffff8801c8171000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 25.220547] ================================================================== [ 25.227873] Disabling lock debugging due to kernel taint [ 25.233599] Kernel panic - not syncing: panic_on_warn set ... [ 25.233599] [ 25.240968] CPU: 1 PID: 3791 Comm: syz-executor676 Tainted: G B 4.9.110-g00a0bcb #56 [ 25.249948] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 25.259284] ffff8801d9657c10 ffffffff81eb2329 ffffffff843c7167 00000000ffffffff [ 25.267299] 0000000000000000 0000000000000001 ffffffff83011be0 ffff8801d9657cd0 [ 25.275300] ffffffff81421925 0000000041b58ab3 ffffffff843ba880 ffffffff81421766 [ 25.283295] Call Trace: [ 25.285861] [] dump_stack+0xc1/0x128 [ 25.291209] [] ? sock_release+0x1c0/0x1c0 [ 25.296985] [] panic+0x1bf/0x3bc [ 25.301974] [] ? add_taint.cold.6+0x16/0x16 [ 25.308269] [] ? ___preempt_schedule+0x16/0x18 [ 25.314479] [] kasan_end_report+0x47/0x4f [ 25.320257] [] kasan_report.cold.6+0x76/0x2fe [ 25.326383] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 25.333114] [] __asan_report_load4_noabort+0x14/0x20 [ 25.339840] [] l2tp_session_queue_purge+0xf4/0x100 [ 25.346392] [] ? sock_release+0x1c0/0x1c0 [ 25.352158] [] pppol2tp_release+0x1fb/0x2e0 [ 25.358118] [] sock_release+0x96/0x1c0 [ 25.363625] [] sock_close+0x16/0x20 [ 25.368872] [] __fput+0x263/0x700 [ 25.373945] [] ____fput+0x15/0x20 [ 25.379025] [] task_work_run+0x10c/0x180 [ 25.384715] [] exit_to_usermode_loop+0xfc/0x120 [ 25.391004] [] do_syscall_64+0x364/0x490 [ 25.396690] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 25.404071] Dumping ftrace buffer: [ 25.407587] (ftrace buffer empty) [ 25.411274] Kernel Offset: disabled [ 25.414882] Rebooting in 86400 seconds..