[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 16.056128] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 21.631036] random: sshd: uninitialized urandom read (32 bytes read) [ 21.855546] random: sshd: uninitialized urandom read (32 bytes read) [ 22.717406] random: sshd: uninitialized urandom read (32 bytes read) [ 22.870074] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.25' (ECDSA) to the list of known hosts. [ 28.372950] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 28.517917] ================================================================== [ 28.525318] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 28.532567] Read of size 4 at addr ffff8801b7954500 by task syz-executor507/3799 [ 28.540093] [ 28.541700] CPU: 0 PID: 3799 Comm: syz-executor507 Not tainted 4.9.111-g03c70fe #57 [ 28.549469] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 28.558812] ffff8801d97f7cb0 ffffffff81eb2729 ffffea0006de5500 ffff8801b7954500 [ 28.566834] 0000000000000000 ffff8801b7954500 ffffffff83012be0 ffff8801d97f7ce8 [ 28.574854] ffffffff81567b59 ffff8801b7954500 0000000000000004 0000000000000000 [ 28.582872] Call Trace: [ 28.585438] [] dump_stack+0xc1/0x128 [ 28.590786] [] ? sock_release+0x1c0/0x1c0 [ 28.596565] [] print_address_description+0x6c/0x234 [ 28.603220] [] ? sock_release+0x1c0/0x1c0 [ 28.609004] [] kasan_report.cold.6+0x242/0x2fe [ 28.615216] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 28.621973] [] __asan_report_load4_noabort+0x14/0x20 [ 28.628708] [] l2tp_session_queue_purge+0xf4/0x100 [ 28.635265] [] ? sock_release+0x1c0/0x1c0 [ 28.641050] [] pppol2tp_release+0x1fb/0x2e0 [ 28.647005] [] sock_release+0x96/0x1c0 [ 28.652519] [] sock_close+0x16/0x20 [ 28.657778] [] __fput+0x263/0x700 [ 28.662860] [] ____fput+0x15/0x20 [ 28.667937] [] task_work_run+0x10c/0x180 [ 28.673624] [] exit_to_usermode_loop+0xfc/0x120 [ 28.679928] [] do_syscall_64+0x364/0x490 [ 28.685623] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.692521] [ 28.694125] Allocated by task 3798: [ 28.697741] save_stack_trace+0x16/0x20 [ 28.701711] save_stack+0x43/0xd0 [ 28.705140] kasan_kmalloc+0xc7/0xe0 [ 28.708829] __kmalloc+0x11d/0x300 [ 28.712347] l2tp_session_create+0x38/0x16f0 [ 28.716738] pppol2tp_connect+0x10d7/0x18f0 [ 28.721061] SYSC_connect+0x1b8/0x300 [ 28.724861] SyS_connect+0x24/0x30 [ 28.728379] do_syscall_64+0x1a6/0x490 [ 28.732258] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.737351] [ 28.738986] Freed by task 3798: [ 28.742243] save_stack_trace+0x16/0x20 [ 28.746190] save_stack+0x43/0xd0 [ 28.749616] kasan_slab_free+0x72/0xc0 [ 28.753477] kfree+0xfb/0x310 [ 28.756554] l2tp_session_free+0x166/0x200 [ 28.760761] l2tp_tunnel_closeall+0x284/0x350 [ 28.765239] l2tp_udp_encap_destroy+0x87/0xe0 [ 28.769713] udpv6_destroy_sock+0xb1/0xd0 [ 28.773839] sk_common_release+0x6d/0x300 [ 28.777960] udp_lib_close+0x15/0x20 [ 28.781651] inet_release+0xff/0x1d0 [ 28.785355] inet6_release+0x50/0x70 [ 28.789044] sock_release+0x96/0x1c0 [ 28.792739] sock_close+0x16/0x20 [ 28.796168] __fput+0x263/0x700 [ 28.799421] ____fput+0x15/0x20 [ 28.802679] task_work_run+0x10c/0x180 [ 28.806543] exit_to_usermode_loop+0xfc/0x120 [ 28.811027] do_syscall_64+0x364/0x490 [ 28.814890] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.819961] [ 28.821649] The buggy address belongs to the object at ffff8801b7954500 [ 28.821649] which belongs to the cache kmalloc-512 of size 512 [ 28.834282] The buggy address is located 0 bytes inside of [ 28.834282] 512-byte region [ffff8801b7954500, ffff8801b7954700) [ 28.845954] The buggy address belongs to the page: [ 28.850855] page:ffffea0006de5500 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 28.861031] flags: 0x8000000000004080(slab|head) [ 28.865769] page dumped because: kasan: bad access detected [ 28.871450] [ 28.873063] Memory state around the buggy address: [ 28.877968] ffff8801b7954400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.885301] ffff8801b7954480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 28.892645] >ffff8801b7954500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.900000] ^ [ 28.903351] ffff8801b7954580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.910703] ffff8801b7954600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.918036] ================================================================== [ 28.925371] Disabling lock debugging due to kernel taint [ 28.930931] Kernel panic - not syncing: panic_on_warn set ... [ 28.930931] [ 28.938378] CPU: 0 PID: 3799 Comm: syz-executor507 Tainted: G B 4.9.111-g03c70fe #57 [ 28.947359] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 28.956692] ffff8801d97f7c10 ffffffff81eb2729 ffffffff843c71a7 00000000ffffffff [ 28.964685] 0000000000000000 0000000000000000 ffffffff83012be0 ffff8801d97f7cd0 [ 28.972718] ffffffff814219f5 0000000041b58ab3 ffffffff843ba8c0 ffffffff81421836 [ 28.980723] Call Trace: [ 28.983300] [] dump_stack+0xc1/0x128 [ 28.988736] [] ? sock_release+0x1c0/0x1c0 [ 28.994510] [] panic+0x1bf/0x3bc [ 28.999510] [] ? add_taint.cold.6+0x16/0x16 [ 29.005464] [] ? ___preempt_schedule+0x16/0x18 [ 29.011719] [] kasan_end_report+0x47/0x4f [ 29.017515] [] kasan_report.cold.6+0x76/0x2fe [ 29.023661] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 29.030408] [] __asan_report_load4_noabort+0x14/0x20 [ 29.037151] [] l2tp_session_queue_purge+0xf4/0x100 [ 29.043716] [] ? sock_release+0x1c0/0x1c0 [ 29.049494] [] pppol2tp_release+0x1fb/0x2e0 [ 29.055449] [] sock_release+0x96/0x1c0 [ 29.060967] [] sock_close+0x16/0x20 [ 29.066224] [] __fput+0x263/0x700 [ 29.071307] [] ____fput+0x15/0x20 [ 29.076393] [] task_work_run+0x10c/0x180 [ 29.082102] [] exit_to_usermode_loop+0xfc/0x120 [ 29.088407] [] do_syscall_64+0x364/0x490 [ 29.094096] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 29.101563] Dumping ftrace buffer: [ 29.105106] (ftrace buffer empty) [ 29.108807] Kernel Offset: disabled [ 29.112411] Rebooting in 86400 seconds..