[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 15.344381] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 21.241996] random: sshd: uninitialized urandom read (32 bytes read) [ 21.641509] random: sshd: uninitialized urandom read (32 bytes read) [ 22.326484] random: sshd: uninitialized urandom read (32 bytes read) [ 24.192238] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.1' (ECDSA) to the list of known hosts. [ 29.609347] 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 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 [ 32.413256] ================================================================== [ 32.420643] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 32.427889] Read of size 4 at addr ffff8801c3d60a00 by task syz-executor754/4936 [ 32.435388] [ 32.436991] CPU: 1 PID: 4936 Comm: syz-executor754 Not tainted 4.9.103-g0cecdf8 #38 [ 32.444753] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 32.454082] ffff8801d856f878 ffffffff81eb34a9 ffffea00070f5800 ffff8801c3d60a00 [ 32.462069] 0000000000000000 ffff8801c3d60a00 ffffffff83012be0 ffff8801d856f8b0 [ 32.470054] ffffffff815676bb ffff8801c3d60a00 0000000000000004 0000000000000000 [ 32.478064] Call Trace: [ 32.480634] [] dump_stack+0xc1/0x128 [ 32.485970] [] ? sock_release+0x1c0/0x1c0 [ 32.491740] [] print_address_description+0x6c/0x234 [ 32.498387] [] ? sock_release+0x1c0/0x1c0 [ 32.504155] [] kasan_report.cold.6+0x242/0x2fe [ 32.510361] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 32.517094] [] __asan_report_load4_noabort+0x14/0x20 [ 32.523829] [] l2tp_session_queue_purge+0xf4/0x100 [ 32.530378] [] ? sock_release+0x1c0/0x1c0 [ 32.536369] [] pppol2tp_release+0x1fb/0x2e0 [ 32.542311] [] sock_release+0x96/0x1c0 [ 32.547819] [] sock_close+0x16/0x20 [ 32.553066] [] __fput+0x263/0x700 [ 32.558138] [] ____fput+0x15/0x20 [ 32.563212] [] task_work_run+0x10c/0x180 [ 32.568895] [] do_exit+0x9e1/0x27c0 [ 32.574149] [] ? debug_check_no_locks_freed+0x210/0x210 [ 32.581138] [] ? get_futex_key+0x1090/0x1090 [ 32.587168] [] ? __lock_acquire+0x654/0x4070 [ 32.593199] [] ? release_task.part.19+0x1210/0x1210 [ 32.599835] [] ? debug_check_no_locks_freed+0x210/0x210 [ 32.606819] [] ? recalc_sigpending+0x72/0x90 [ 32.612861] [] do_group_exit+0x111/0x340 [ 32.618545] [] get_signal+0x4cf/0x1450 [ 32.624054] [] do_signal+0x87/0x19f0 [ 32.629385] [] ? __fd_install+0x24a/0x5d0 [ 32.635152] [] ? get_unused_fd_flags+0xd0/0xd0 [ 32.641362] [] ? get_unused_fd_flags+0xd0/0xd0 [ 32.647563] [] ? setup_sigcontext+0x7d0/0x7d0 [ 32.653677] [] ? fd_install+0x4d/0x60 [ 32.659099] [] ? do_futex+0x17c0/0x17c0 [ 32.664696] [] ? SyS_socket+0x121/0x1b0 [ 32.670290] [] ? exit_to_usermode_loop+0xac/0x120 [ 32.676753] [] exit_to_usermode_loop+0xe1/0x120 [ 32.683049] [] do_syscall_64+0x364/0x490 [ 32.688730] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 32.695624] [ 32.697223] Allocated by task 4933: [ 32.700821] save_stack_trace+0x16/0x20 [ 32.704767] save_stack+0x43/0xd0 [ 32.708189] kasan_kmalloc+0xc7/0xe0 [ 32.711876] __kmalloc+0x11d/0x300 [ 32.715387] l2tp_session_create+0x38/0x16f0 [ 32.719768] pppol2tp_connect+0x10d7/0x18f0 [ 32.724059] SYSC_connect+0x1b8/0x300 [ 32.727829] SyS_connect+0x24/0x30 [ 32.731341] do_syscall_64+0x1a6/0x490 [ 32.735199] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 32.740270] [ 32.741867] Freed by task 4855: [ 32.745203] save_stack_trace+0x16/0x20 [ 32.749148] save_stack+0x43/0xd0 [ 32.752573] kasan_slab_free+0x72/0xc0 [ 32.756433] kfree+0xfb/0x310 [ 32.759514] l2tp_session_free+0x166/0x200 [ 32.763718] l2tp_tunnel_closeall+0x284/0x350 [ 32.768183] l2tp_udp_encap_destroy+0x87/0xe0 [ 32.772650] udpv6_destroy_sock+0xb1/0xd0 [ 32.776769] sk_common_release+0x6d/0x300 [ 32.780887] udp_lib_close+0x15/0x20 [ 32.784573] inet_release+0xff/0x1d0 [ 32.788256] inet6_release+0x50/0x70 [ 32.791942] sock_release+0x96/0x1c0 [ 32.795626] sock_close+0x16/0x20 [ 32.799053] __fput+0x263/0x700 [ 32.802304] ____fput+0x15/0x20 [ 32.805567] task_work_run+0x10c/0x180 [ 32.809427] do_exit+0x9e1/0x27c0 [ 32.812851] do_group_exit+0x111/0x340 [ 32.816715] SyS_exit_group+0x1d/0x20 [ 32.820512] do_syscall_64+0x1a6/0x490 [ 32.824381] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 32.829460] [ 32.831060] The buggy address belongs to the object at ffff8801c3d60a00 [ 32.831060] which belongs to the cache kmalloc-512 of size 512 [ 32.843694] The buggy address is located 0 bytes inside of [ 32.843694] 512-byte region [ffff8801c3d60a00, ffff8801c3d60c00) [ 32.855366] The buggy address belongs to the page: [ 32.860267] page:ffffea00070f5800 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 32.870440] flags: 0x8000000000004080(slab|head) [ 32.875173] page dumped because: kasan: bad access detected [ 32.880852] [ 32.882450] Memory state around the buggy address: [ 32.887351] ffff8801c3d60900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 32.894683] ffff8801c3d60980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 32.902015] >ffff8801c3d60a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 32.909344] ^ [ 32.912682] ffff8801c3d60a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 32.920013] ffff8801c3d60b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 32.927341] ================================================================== [ 32.934669] Disabling lock debugging due to kernel taint [ 32.940372] Kernel panic - not syncing: panic_on_warn set ... [ 32.940372] [ 32.947717] CPU: 1 PID: 4936 Comm: syz-executor754 Tainted: G B 4.9.103-g0cecdf8 #38 [ 32.956696] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 32.966033] ffff8801d856f7d8 ffffffff81eb34a9 ffffffff843c5d75 00000000ffffffff [ 32.974037] 0000000000000000 0000000000000001 ffffffff83012be0 ffff8801d856f898 [ 32.982043] ffffffff81421aa5 0000000041b58ab3 ffffffff843b94a8 ffffffff814218e6 [ 32.990032] Call Trace: [ 32.992597] [] dump_stack+0xc1/0x128 [ 32.997935] [] ? sock_release+0x1c0/0x1c0 [ 33.003707] [] panic+0x1bf/0x3bc [ 33.008697] [] ? add_taint.cold.6+0x16/0x16 [ 33.014641] [] ? ___preempt_schedule+0x16/0x18 [ 33.020845] [] kasan_end_report+0x47/0x4f [ 33.026614] [] kasan_report.cold.6+0x76/0x2fe [ 33.032734] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 33.039461] [] __asan_report_load4_noabort+0x14/0x20 [ 33.046190] [] l2tp_session_queue_purge+0xf4/0x100 [ 33.052744] [] ? sock_release+0x1c0/0x1c0 [ 33.058517] [] pppol2tp_release+0x1fb/0x2e0 [ 33.064462] [] sock_release+0x96/0x1c0 [ 33.069976] [] sock_close+0x16/0x20 [ 33.075228] [] __fput+0x263/0x700 [ 33.080305] [] ____fput+0x15/0x20 [ 33.085381] [] task_work_run+0x10c/0x180 [ 33.091067] [] do_exit+0x9e1/0x27c0 [ 33.096328] [] ? debug_check_no_locks_freed+0x210/0x210 [ 33.103315] [] ? get_futex_key+0x1090/0x1090 [ 33.109348] [] ? __lock_acquire+0x654/0x4070 [ 33.115382] [] ? release_task.part.19+0x1210/0x1210 [ 33.122030] [] ? debug_check_no_locks_freed+0x210/0x210 [ 33.129018] [] ? recalc_sigpending+0x72/0x90 [ 33.135048] [] do_group_exit+0x111/0x340 [ 33.140731] [] get_signal+0x4cf/0x1450 [ 33.146240] [] do_signal+0x87/0x19f0 [ 33.151663] [] ? __fd_install+0x24a/0x5d0 [ 33.157432] [] ? get_unused_fd_flags+0xd0/0xd0 [ 33.163637] [] ? get_unused_fd_flags+0xd0/0xd0 [ 33.169840] [] ? setup_sigcontext+0x7d0/0x7d0 [ 33.175967] [] ? fd_install+0x4d/0x60 [ 33.181393] [] ? do_futex+0x17c0/0x17c0 [ 33.186990] [] ? SyS_socket+0x121/0x1b0 [ 33.192587] [] ? exit_to_usermode_loop+0xac/0x120 [ 33.199051] [] exit_to_usermode_loop+0xe1/0x120 [ 33.205340] [] do_syscall_64+0x364/0x490 [ 33.211023] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 33.218302] Dumping ftrace buffer: [ 33.221814] (ftrace buffer empty) [ 33.225498] Kernel Offset: disabled [ 33.229098] Rebooting in 86400 seconds..