[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 13.717120] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 17.624151] random: sshd: uninitialized urandom read (32 bytes read) [ 18.050499] random: sshd: uninitialized urandom read (32 bytes read) [ 19.093540] random: sshd: uninitialized urandom read (32 bytes read) [ 23.283355] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.31' (ECDSA) to the list of known hosts. [ 28.684110] 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 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 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 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 [ 42.216638] random: crng init done [ 42.294839] ================================================================== [ 42.302250] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 42.309519] Read of size 4 at addr ffff8801bca37b80 by task syz-executor720/4503 [ 42.317032] [ 42.318642] CPU: 1 PID: 4503 Comm: syz-executor720 Not tainted 4.9.107-gdb2c520 #46 [ 42.326427] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 42.335770] ffff8801d7da7cb0 ffffffff81eb3da9 ffffea0006f28d80 ffff8801bca37b80 [ 42.343830] 0000000000000000 ffff8801bca37b80 ffffffff83013be0 ffff8801d7da7ce8 [ 42.351857] ffffffff815679f9 ffff8801bca37b80 0000000000000004 0000000000000000 [ 42.359922] Call Trace: [ 42.362495] [] dump_stack+0xc1/0x128 [ 42.367863] [] ? sock_release+0x1c0/0x1c0 [ 42.373657] [] print_address_description+0x6c/0x234 [ 42.380320] [] ? sock_release+0x1c0/0x1c0 [ 42.386123] [] kasan_report.cold.6+0x242/0x2fe [ 42.392357] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 42.399107] [] __asan_report_load4_noabort+0x14/0x20 [ 42.405875] [] l2tp_session_queue_purge+0xf4/0x100 [ 42.416732] [] ? sock_release+0x1c0/0x1c0 [ 42.422601] [] pppol2tp_release+0x1fb/0x2e0 [ 42.428574] [] sock_release+0x96/0x1c0 [ 42.434098] [] sock_close+0x16/0x20 [ 42.439368] [] __fput+0x263/0x700 [ 42.444453] [] ____fput+0x15/0x20 [ 42.449539] [] task_work_run+0x10c/0x180 [ 42.455252] [] exit_to_usermode_loop+0xfc/0x120 [ 42.461550] [] do_syscall_64+0x364/0x490 [ 42.467248] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 42.474149] [ 42.475754] Allocated by task 4504: [ 42.479356] save_stack_trace+0x16/0x20 [ 42.483302] save_stack+0x43/0xd0 [ 42.486726] kasan_kmalloc+0xc7/0xe0 [ 42.490413] __kmalloc+0x11d/0x300 [ 42.493922] l2tp_session_create+0x38/0x16f0 [ 42.498315] pppol2tp_connect+0x10d7/0x18f0 [ 42.502610] SYSC_connect+0x1b8/0x300 [ 42.506380] SyS_connect+0x24/0x30 [ 42.509890] do_syscall_64+0x1a6/0x490 [ 42.513749] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 42.519002] [ 42.520606] Freed by task 4504: [ 42.523858] save_stack_trace+0x16/0x20 [ 42.527803] save_stack+0x43/0xd0 [ 42.531228] kasan_slab_free+0x72/0xc0 [ 42.535087] kfree+0xfb/0x310 [ 42.538165] l2tp_session_free+0x166/0x200 [ 42.542378] l2tp_tunnel_closeall+0x284/0x350 [ 42.546931] l2tp_udp_encap_destroy+0x87/0xe0 [ 42.551407] udpv6_destroy_sock+0xb1/0xd0 [ 42.555543] sk_common_release+0x6d/0x300 [ 42.560364] udp_lib_close+0x15/0x20 [ 42.564094] inet_release+0xff/0x1d0 [ 42.567798] inet6_release+0x50/0x70 [ 42.571493] sock_release+0x96/0x1c0 [ 42.575202] sock_close+0x16/0x20 [ 42.578633] __fput+0x263/0x700 [ 42.581886] ____fput+0x15/0x20 [ 42.585149] task_work_run+0x10c/0x180 [ 42.589008] exit_to_usermode_loop+0xfc/0x120 [ 42.593476] do_syscall_64+0x364/0x490 [ 42.597335] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 42.602417] [ 42.604024] The buggy address belongs to the object at ffff8801bca37b80 [ 42.604024] which belongs to the cache kmalloc-512 of size 512 [ 42.616666] The buggy address is located 0 bytes inside of [ 42.616666] 512-byte region [ffff8801bca37b80, ffff8801bca37d80) [ 42.628348] The buggy address belongs to the page: [ 42.633273] page:ffffea0006f28d80 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 42.643491] flags: 0x8000000000004080(slab|head) [ 42.648218] page dumped because: kasan: bad access detected [ 42.653897] [ 42.655496] Memory state around the buggy address: [ 42.660397] ffff8801bca37a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 42.667727] ffff8801bca37b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 42.675067] >ffff8801bca37b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 42.682397] ^ [ 42.685745] ffff8801bca37c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 42.693077] ffff8801bca37c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 42.700414] ================================================================== [ 42.707746] Disabling lock debugging due to kernel taint [ 42.713841] Kernel panic - not syncing: panic_on_warn set ... [ 42.713841] [ 42.721184] CPU: 1 PID: 4503 Comm: syz-executor720 Tainted: G B 4.9.107-gdb2c520 #46 [ 42.730161] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 42.739491] ffff8801d7da7c10 ffffffff81eb3da9 ffffffff843c6427 00000000ffffffff [ 42.747478] 0000000000000000 0000000000000001 ffffffff83013be0 ffff8801d7da7cd0 [ 42.755604] ffffffff81421925 0000000041b58ab3 ffffffff843b9b48 ffffffff81421766 [ 42.763753] Call Trace: [ 42.766327] [] dump_stack+0xc1/0x128 [ 42.771663] [] ? sock_release+0x1c0/0x1c0 [ 42.777433] [] panic+0x1bf/0x3bc [ 42.782427] [] ? add_taint.cold.6+0x16/0x16 [ 42.788369] [] ? ___preempt_schedule+0x16/0x18 [ 42.794574] [] kasan_end_report+0x47/0x4f [ 42.800349] [] kasan_report.cold.6+0x76/0x2fe [ 42.806474] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 42.813200] [] __asan_report_load4_noabort+0x14/0x20 [ 42.819923] [] l2tp_session_queue_purge+0xf4/0x100 [ 42.826480] [] ? sock_release+0x1c0/0x1c0 [ 42.832249] [] pppol2tp_release+0x1fb/0x2e0 [ 42.838203] [] sock_release+0x96/0x1c0 [ 42.846143] [] sock_close+0x16/0x20 [ 42.851392] [] __fput+0x263/0x700 [ 42.856464] [] ____fput+0x15/0x20 [ 42.861545] [] task_work_run+0x10c/0x180 [ 42.867227] [] exit_to_usermode_loop+0xfc/0x120 [ 42.874045] [] do_syscall_64+0x364/0x490 [ 42.879736] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 42.887316] Dumping ftrace buffer: [ 42.890839] (ftrace buffer empty) [ 42.894696] Kernel Offset: disabled [ 42.898404] Rebooting in 86400 seconds..