[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 12.761486] 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: [ 16.648819] random: sshd: uninitialized urandom read (32 bytes read) [ 16.988197] random: sshd: uninitialized urandom read (32 bytes read) [ 18.077537] random: sshd: uninitialized urandom read (32 bytes read) [ 18.170674] random: crng init done Warning: Permanently added '10.128.10.40' (ECDSA) to the list of known hosts. 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 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 [ 33.501226] ================================================================== [ 33.508644] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 33.515898] Read of size 4 at addr ffff8801c93ae280 by task syz-executor223/4056 [ 33.523401] [ 33.525011] CPU: 1 PID: 4056 Comm: syz-executor223 Not tainted 4.9.109-ga4230be #51 [ 33.532775] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 33.542105] ffff8801d8437b00 ffffffff81eb3e29 ffffea000724eb80 ffff8801c93ae280 [ 33.550098] 0000000000000000 ffff8801c93ae280 ffffffff83013be0 ffff8801d8437b38 [ 33.558130] ffffffff81567a89 ffff8801c93ae280 0000000000000004 0000000000000000 [ 33.566109] Call Trace: [ 33.568668] [] dump_stack+0xc1/0x128 [ 33.574014] [] ? sock_release+0x1c0/0x1c0 [ 33.579785] [] print_address_description+0x6c/0x234 [ 33.586428] [] ? sock_release+0x1c0/0x1c0 [ 33.592199] [] kasan_report.cold.6+0x242/0x2fe [ 33.598409] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 33.605144] [] __asan_report_load4_noabort+0x14/0x20 [ 33.611880] [] l2tp_session_queue_purge+0xf4/0x100 [ 33.618433] [] ? sock_release+0x1c0/0x1c0 [ 33.624202] [] pppol2tp_release+0x1fb/0x2e0 [ 33.630146] [] sock_release+0x96/0x1c0 [ 33.635658] [] sock_close+0x16/0x20 [ 33.640910] [] __fput+0x263/0x700 [ 33.645993] [] ____fput+0x15/0x20 [ 33.651072] [] task_work_run+0x10c/0x180 [ 33.656760] [] do_exit+0x9e1/0x27c0 [ 33.662020] [] ? vm_insert_mixed+0x200/0x200 [ 33.668052] [] ? release_task.part.19+0x1210/0x1210 [ 33.674710] [] ? __do_page_fault+0x5dd/0xd50 [ 33.680745] [] ? up_read+0x1a/0x40 [ 33.685911] [] ? __do_page_fault+0x183/0xd50 [ 33.691942] [] do_group_exit+0x111/0x340 [ 33.697627] [] ? do_group_exit+0x340/0x340 [ 33.703484] [] SyS_exit_group+0x1d/0x20 [ 33.709092] [] do_syscall_64+0x1a6/0x490 [ 33.714778] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 33.721675] [ 33.723275] Allocated by task 4054: [ 33.726877] save_stack_trace+0x16/0x20 [ 33.730824] save_stack+0x43/0xd0 [ 33.734247] kasan_kmalloc+0xc7/0xe0 [ 33.737936] __kmalloc+0x11d/0x300 [ 33.741460] l2tp_session_create+0x38/0x16f0 [ 33.745847] pppol2tp_connect+0x10d7/0x18f0 [ 33.750145] SYSC_connect+0x1b8/0x300 [ 33.753927] SyS_connect+0x24/0x30 [ 33.757439] do_syscall_64+0x1a6/0x490 [ 33.761308] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 33.766379] [ 33.767977] Freed by task 4026: [ 33.771233] save_stack_trace+0x16/0x20 [ 33.775180] save_stack+0x43/0xd0 [ 33.778605] kasan_slab_free+0x72/0xc0 [ 33.782464] kfree+0xfb/0x310 [ 33.785545] l2tp_session_free+0x166/0x200 [ 33.789748] l2tp_tunnel_closeall+0x284/0x350 [ 33.794211] l2tp_udp_encap_destroy+0x87/0xe0 [ 33.798930] udpv6_destroy_sock+0xb1/0xd0 [ 33.803063] sk_common_release+0x6d/0x300 [ 33.807183] udp_lib_close+0x15/0x20 [ 33.810883] inet_release+0xff/0x1d0 [ 33.814568] inet6_release+0x50/0x70 [ 33.818251] sock_release+0x96/0x1c0 [ 33.821946] sock_close+0x16/0x20 [ 33.825369] __fput+0x263/0x700 [ 33.828621] ____fput+0x15/0x20 [ 33.831871] task_work_run+0x10c/0x180 [ 33.835727] do_exit+0x9e1/0x27c0 [ 33.839152] do_group_exit+0x111/0x340 [ 33.843011] SyS_exit_group+0x1d/0x20 [ 33.846793] do_syscall_64+0x1a6/0x490 [ 33.850652] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 33.855726] [ 33.857325] The buggy address belongs to the object at ffff8801c93ae280 [ 33.857325] which belongs to the cache kmalloc-512 of size 512 [ 33.869961] The buggy address is located 0 bytes inside of [ 33.869961] 512-byte region [ffff8801c93ae280, ffff8801c93ae480) [ 33.881645] The buggy address belongs to the page: [ 33.886549] page:ffffea000724eb80 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 33.896737] flags: 0x8000000000004080(slab|head) [ 33.901459] page dumped because: kasan: bad access detected [ 33.907137] [ 33.908736] Memory state around the buggy address: [ 33.913645] ffff8801c93ae180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 33.920978] ffff8801c93ae200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 33.928310] >ffff8801c93ae280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 33.935642] ^ [ 33.938983] ffff8801c93ae300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 33.946317] ffff8801c93ae380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 33.953645] ================================================================== [ 33.960975] Disabling lock debugging due to kernel taint [ 33.966669] Kernel panic - not syncing: panic_on_warn set ... [ 33.966669] [ 33.974279] CPU: 1 PID: 4056 Comm: syz-executor223 Tainted: G B 4.9.109-ga4230be #51 [ 33.983261] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 33.992590] ffff8801d8437a60 ffffffff81eb3e29 ffffffff843c6327 00000000ffffffff [ 34.000589] 0000000000000000 0000000000000001 ffffffff83013be0 ffff8801d8437b20 [ 34.008562] ffffffff81421925 0000000041b58ab3 ffffffff843b9a40 ffffffff81421766 [ 34.016557] Call Trace: [ 34.019127] [] dump_stack+0xc1/0x128 [ 34.024471] [] ? sock_release+0x1c0/0x1c0 [ 34.030274] [] panic+0x1bf/0x3bc [ 34.035263] [] ? add_taint.cold.6+0x16/0x16 [ 34.041207] [] ? ___preempt_schedule+0x16/0x18 [ 34.047410] [] kasan_end_report+0x47/0x4f [ 34.053180] [] kasan_report.cold.6+0x76/0x2fe [ 34.059299] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 34.066034] [] __asan_report_load4_noabort+0x14/0x20 [ 34.072771] [] l2tp_session_queue_purge+0xf4/0x100 [ 34.079322] [] ? sock_release+0x1c0/0x1c0 [ 34.085100] [] pppol2tp_release+0x1fb/0x2e0 [ 34.091042] [] sock_release+0x96/0x1c0 [ 34.096549] [] sock_close+0x16/0x20 [ 34.101800] [] __fput+0x263/0x700 [ 34.106877] [] ____fput+0x15/0x20 [ 34.111965] [] task_work_run+0x10c/0x180 [ 34.117648] [] do_exit+0x9e1/0x27c0 [ 34.122898] [] ? vm_insert_mixed+0x200/0x200 [ 34.128930] [] ? release_task.part.19+0x1210/0x1210 [ 34.135570] [] ? __do_page_fault+0x5dd/0xd50 [ 34.141599] [] ? up_read+0x1a/0x40 [ 34.146770] [] ? __do_page_fault+0x183/0xd50 [ 34.152802] [] do_group_exit+0x111/0x340 [ 34.158487] [] ? do_group_exit+0x340/0x340 [ 34.164344] [] SyS_exit_group+0x1d/0x20 [ 34.169942] [] do_syscall_64+0x1a6/0x490 [ 34.175635] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 34.182966] Dumping ftrace buffer: [ 34.186477] (ftrace buffer empty) [ 34.190161] Kernel Offset: disabled [ 34.193759] Rebooting in 86400 seconds..