[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 14.429024] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 20.555462] random: sshd: uninitialized urandom read (32 bytes read) [ 20.909474] random: sshd: uninitialized urandom read (32 bytes read) [ 21.872849] random: sshd: uninitialized urandom read (32 bytes read) [ 29.138843] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.54' (ECDSA) to the list of known hosts. [ 34.665088] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 34.827744] ================================================================== [ 34.835152] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 34.842409] Read of size 4 at addr ffff8801c8c2d680 by task syz-executor957/3789 [ 34.849912] [ 34.851530] CPU: 1 PID: 3789 Comm: syz-executor957 Not tainted 4.9.113-g9905591 #66 [ 34.859294] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 34.868639] ffff8801d8c3fcb0 ffffffff81eb32a9 ffffea0007230b00 ffff8801c8c2d680 [ 34.876654] 0000000000000000 ffff8801c8c2d680 ffffffff83013be0 ffff8801d8c3fce8 [ 34.884674] ffffffff81567bd9 ffff8801c8c2d680 0000000000000004 0000000000000000 [ 34.892665] Call Trace: [ 34.895230] [] dump_stack+0xc1/0x128 [ 34.900573] [] ? sock_release+0x1c0/0x1c0 [ 34.906364] [] print_address_description+0x6c/0x234 [ 34.913006] [] ? sock_release+0x1c0/0x1c0 [ 34.918779] [] kasan_report.cold.6+0x242/0x2fe [ 34.924988] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 34.931717] [] __asan_report_load4_noabort+0x14/0x20 [ 34.938442] [] l2tp_session_queue_purge+0xf4/0x100 [ 34.945012] [] ? sock_release+0x1c0/0x1c0 [ 34.950786] [] pppol2tp_release+0x1fb/0x2e0 [ 34.956733] [] sock_release+0x96/0x1c0 [ 34.962246] [] sock_close+0x16/0x20 [ 34.967499] [] __fput+0x263/0x700 [ 34.972573] [] ____fput+0x15/0x20 [ 34.977653] [] task_work_run+0x10c/0x180 [ 34.983339] [] exit_to_usermode_loop+0xfc/0x120 [ 34.989636] [] do_syscall_64+0x364/0x490 [ 34.995342] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 35.002248] [ 35.003851] Allocated by task 3790: [ 35.007459] save_stack_trace+0x16/0x20 [ 35.011408] save_stack+0x43/0xd0 [ 35.014835] kasan_kmalloc+0xc7/0xe0 [ 35.018527] __kmalloc+0x11d/0x300 [ 35.022041] l2tp_session_create+0x38/0x16f0 [ 35.026422] pppol2tp_connect+0x10d7/0x18f0 [ 35.030722] SYSC_connect+0x1b8/0x300 [ 35.034495] SyS_connect+0x24/0x30 [ 35.038008] do_syscall_64+0x1a6/0x490 [ 35.041874] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 35.046950] [ 35.048553] Freed by task 3790: [ 35.051809] save_stack_trace+0x16/0x20 [ 35.055758] save_stack+0x43/0xd0 [ 35.059186] kasan_slab_free+0x72/0xc0 [ 35.063063] kfree+0xfb/0x310 [ 35.066146] l2tp_session_free+0x166/0x200 [ 35.070370] l2tp_tunnel_closeall+0x284/0x350 [ 35.074840] l2tp_udp_encap_destroy+0x87/0xe0 [ 35.079308] udpv6_destroy_sock+0xb1/0xd0 [ 35.083432] sk_common_release+0x6d/0x300 [ 35.087553] udp_lib_close+0x15/0x20 [ 35.091243] inet_release+0xff/0x1d0 [ 35.094932] inet6_release+0x50/0x70 [ 35.098622] sock_release+0x96/0x1c0 [ 35.102311] sock_close+0x16/0x20 [ 35.105742] __fput+0x263/0x700 [ 35.108994] ____fput+0x15/0x20 [ 35.112249] task_work_run+0x10c/0x180 [ 35.116123] exit_to_usermode_loop+0xfc/0x120 [ 35.120594] do_syscall_64+0x364/0x490 [ 35.124467] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 35.129542] [ 35.131148] The buggy address belongs to the object at ffff8801c8c2d680 [ 35.131148] which belongs to the cache kmalloc-512 of size 512 [ 35.143792] The buggy address is located 0 bytes inside of [ 35.143792] 512-byte region [ffff8801c8c2d680, ffff8801c8c2d880) [ 35.155475] The buggy address belongs to the page: [ 35.160381] page:ffffea0007230b00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 35.170574] flags: 0x8000000000004080(slab|head) [ 35.175301] page dumped because: kasan: bad access detected [ 35.180990] [ 35.182588] Memory state around the buggy address: [ 35.188130] ffff8801c8c2d580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 35.195470] ffff8801c8c2d600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 35.202802] >ffff8801c8c2d680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 35.210148] ^ [ 35.213488] ffff8801c8c2d700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 35.220822] ffff8801c8c2d780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 35.228153] ================================================================== [ 35.235498] Disabling lock debugging due to kernel taint [ 35.241055] Kernel panic - not syncing: panic_on_warn set ... [ 35.241055] [ 35.248402] CPU: 1 PID: 3789 Comm: syz-executor957 Tainted: G B 4.9.113-g9905591 #66 [ 35.257386] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 35.266723] ffff8801d8c3fc10 ffffffff81eb32a9 ffffffff843c806f 00000000ffffffff [ 35.274710] 0000000000000000 0000000000000001 ffffffff83013be0 ffff8801d8c3fcd0 [ 35.282695] ffffffff81421a55 0000000041b58ab3 ffffffff843bb788 ffffffff81421896 [ 35.290680] Call Trace: [ 35.293246] [] dump_stack+0xc1/0x128 [ 35.298586] [] ? sock_release+0x1c0/0x1c0 [ 35.304370] [] panic+0x1bf/0x3bc [ 35.309369] [] ? add_taint.cold.6+0x16/0x16 [ 35.315318] [] ? ___preempt_schedule+0x16/0x18 [ 35.321525] [] kasan_end_report+0x47/0x4f [ 35.327293] [] kasan_report.cold.6+0x76/0x2fe [ 35.333416] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 35.340145] [] __asan_report_load4_noabort+0x14/0x20 [ 35.346886] [] l2tp_session_queue_purge+0xf4/0x100 [ 35.353442] [] ? sock_release+0x1c0/0x1c0 [ 35.359227] [] pppol2tp_release+0x1fb/0x2e0 [ 35.365173] [] sock_release+0x96/0x1c0 [ 35.370685] [] sock_close+0x16/0x20 [ 35.375938] [] __fput+0x263/0x700 [ 35.381017] [] ____fput+0x15/0x20 [ 35.386113] [] task_work_run+0x10c/0x180 [ 35.391797] [] exit_to_usermode_loop+0xfc/0x120 [ 35.398101] [] do_syscall_64+0x364/0x490 [ 35.403962] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 35.411314] Dumping ftrace buffer: [ 35.414830] (ftrace buffer empty) [ 35.418520] Kernel Offset: disabled [ 35.422139] Rebooting in 86400 seconds..