[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 13.421114] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 19.252853] random: sshd: uninitialized urandom read (32 bytes read) [ 19.479687] random: sshd: uninitialized urandom read (32 bytes read) [ 20.369545] random: sshd: uninitialized urandom read (32 bytes read) [ 33.658478] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.45' (ECDSA) to the list of known hosts. [ 39.330739] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 39.467192] ================================================================== [ 39.474613] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 39.481882] Read of size 4 at addr ffff8801ca7a4f00 by task syz-executor383/3812 [ 39.489401] [ 39.491021] CPU: 1 PID: 3812 Comm: syz-executor383 Not tainted 4.9.112-g9e79039 #59 [ 39.498793] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 39.508139] ffff8801d8ec7cb0 ffffffff81eb3249 ffffea000729e900 ffff8801ca7a4f00 [ 39.516143] 0000000000000000 ffff8801ca7a4f00 ffffffff83013be0 ffff8801d8ec7ce8 [ 39.524152] ffffffff81567bd9 ffff8801ca7a4f00 0000000000000004 0000000000000000 [ 39.532154] Call Trace: [ 39.534728] [] dump_stack+0xc1/0x128 [ 39.540075] [] ? sock_release+0x1c0/0x1c0 [ 39.545867] [] print_address_description+0x6c/0x234 [ 39.552525] [] ? sock_release+0x1c0/0x1c0 [ 39.558411] [] kasan_report.cold.6+0x242/0x2fe [ 39.564648] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 39.571386] [] __asan_report_load4_noabort+0x14/0x20 [ 39.578118] [] l2tp_session_queue_purge+0xf4/0x100 [ 39.584702] [] ? sock_release+0x1c0/0x1c0 [ 39.590480] [] pppol2tp_release+0x1fb/0x2e0 [ 39.596430] [] sock_release+0x96/0x1c0 [ 39.601946] [] sock_close+0x16/0x20 [ 39.607202] [] __fput+0x263/0x700 [ 39.612284] [] ____fput+0x15/0x20 [ 39.617471] [] task_work_run+0x10c/0x180 [ 39.623172] [] exit_to_usermode_loop+0xfc/0x120 [ 39.629469] [] do_syscall_64+0x364/0x490 [ 39.635159] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 39.642061] [ 39.643670] Allocated by task 3811: [ 39.647274] save_stack_trace+0x16/0x20 [ 39.651313] save_stack+0x43/0xd0 [ 39.654915] kasan_kmalloc+0xc7/0xe0 [ 39.658604] __kmalloc+0x11d/0x300 [ 39.662135] l2tp_session_create+0x38/0x16f0 [ 39.667558] pppol2tp_connect+0x10d7/0x18f0 [ 39.671858] SYSC_connect+0x1b8/0x300 [ 39.675732] SyS_connect+0x24/0x30 [ 39.679335] do_syscall_64+0x1a6/0x490 [ 39.683198] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 39.688556] [ 39.690165] Freed by task 3811: [ 39.693424] save_stack_trace+0x16/0x20 [ 39.697376] save_stack+0x43/0xd0 [ 39.700807] kasan_slab_free+0x72/0xc0 [ 39.704814] kfree+0xfb/0x310 [ 39.707897] l2tp_session_free+0x166/0x200 [ 39.712110] l2tp_tunnel_closeall+0x284/0x350 [ 39.716579] l2tp_udp_encap_destroy+0x87/0xe0 [ 39.721863] udp_destroy_sock+0x118/0x1a0 [ 39.725989] sk_common_release+0x6d/0x300 [ 39.730115] udp_lib_close+0x15/0x20 [ 39.733811] inet_release+0xff/0x1d0 [ 39.737504] sock_release+0x96/0x1c0 [ 39.741196] sock_close+0x16/0x20 [ 39.744634] __fput+0x263/0x700 [ 39.747888] ____fput+0x15/0x20 [ 39.751145] task_work_run+0x10c/0x180 [ 39.755027] exit_to_usermode_loop+0xfc/0x120 [ 39.759510] do_syscall_64+0x364/0x490 [ 39.763392] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 39.768473] [ 39.770086] The buggy address belongs to the object at ffff8801ca7a4f00 [ 39.770086] which belongs to the cache kmalloc-512 of size 512 [ 39.782753] The buggy address is located 0 bytes inside of [ 39.782753] 512-byte region [ffff8801ca7a4f00, ffff8801ca7a5100) [ 39.794431] The buggy address belongs to the page: [ 39.799340] page:ffffea000729e900 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 39.809549] flags: 0x8000000000004080(slab|head) [ 39.814289] page dumped because: kasan: bad access detected [ 39.819975] [ 39.821586] Memory state around the buggy address: [ 39.826504] ffff8801ca7a4e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 39.833841] ffff8801ca7a4e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 39.841177] >ffff8801ca7a4f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 39.848511] ^ [ 39.851855] ffff8801ca7a4f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 39.859195] ffff8801ca7a5000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 39.866620] ================================================================== [ 39.873957] Disabling lock debugging due to kernel taint [ 39.879955] Kernel panic - not syncing: panic_on_warn set ... [ 39.879955] [ 39.887307] CPU: 1 PID: 3812 Comm: syz-executor383 Tainted: G B 4.9.112-g9e79039 #59 [ 39.896308] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 39.905667] ffff8801d8ec7c10 ffffffff81eb3249 ffffffff843c775f 00000000ffffffff [ 39.913767] 0000000000000000 0000000000000001 ffffffff83013be0 ffff8801d8ec7cd0 [ 39.921769] ffffffff81421a55 0000000041b58ab3 ffffffff843bae78 ffffffff81421896 [ 39.929789] Call Trace: [ 39.932366] [] dump_stack+0xc1/0x128 [ 39.937708] [] ? sock_release+0x1c0/0x1c0 [ 39.943487] [] panic+0x1bf/0x3bc [ 39.948494] [] ? add_taint.cold.6+0x16/0x16 [ 39.954459] [] ? ___preempt_schedule+0x16/0x18 [ 39.960687] [] kasan_end_report+0x47/0x4f [ 39.966482] [] kasan_report.cold.6+0x76/0x2fe [ 39.972617] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 39.979344] [] __asan_report_load4_noabort+0x14/0x20 [ 39.986081] [] l2tp_session_queue_purge+0xf4/0x100 [ 39.992650] [] ? sock_release+0x1c0/0x1c0 [ 39.998422] [] pppol2tp_release+0x1fb/0x2e0 [ 40.004371] [] sock_release+0x96/0x1c0 [ 40.009895] [] sock_close+0x16/0x20 [ 40.015148] [] __fput+0x263/0x700 [ 40.020244] [] ____fput+0x15/0x20 [ 40.025336] [] task_work_run+0x10c/0x180 [ 40.031031] [] exit_to_usermode_loop+0xfc/0x120 [ 40.037325] [] do_syscall_64+0x364/0x490 [ 40.043011] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 40.050416] Dumping ftrace buffer: [ 40.053931] (ftrace buffer empty) [ 40.057616] Kernel Offset: disabled [ 40.061220] Rebooting in 86400 seconds..