[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 12.794879] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 15.318047] random: sshd: uninitialized urandom read (32 bytes read) [ 15.613472] random: sshd: uninitialized urandom read (32 bytes read) [ 16.429478] random: sshd: uninitialized urandom read (32 bytes read) [ 16.559521] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.25' (ECDSA) to the list of known hosts. [ 22.035474] 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 executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program [ 26.939163] ================================================================== [ 26.946561] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 26.953808] Read of size 4 at addr ffff8801c5aea780 by task syz-executor898/5004 [ 26.961309] [ 26.962910] CPU: 1 PID: 5004 Comm: syz-executor898 Not tainted 4.9.100-g73fdfa3 #26 [ 26.970669] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 26.979994] ffff8801d80a7b00 ffffffff81eb0f09 ffffea000716ba80 ffff8801c5aea780 [ 26.987968] 0000000000000000 ffff8801c5aea780 ffffffff8300fbe0 ffff8801d80a7b38 [ 26.995944] ffffffff8156532b ffff8801c5aea780 0000000000000004 0000000000000000 [ 27.003926] Call Trace: [ 27.006486] [] dump_stack+0xc1/0x128 [ 27.011820] [] ? sock_release+0x1c0/0x1c0 [ 27.017590] [] print_address_description+0x6c/0x234 [ 27.024228] [] ? sock_release+0x1c0/0x1c0 [ 27.030000] [] kasan_report.cold.6+0x242/0x2fe [ 27.036204] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 27.042929] [] __asan_report_load4_noabort+0x14/0x20 [ 27.049657] [] l2tp_session_queue_purge+0xf4/0x100 [ 27.056207] [] ? sock_release+0x1c0/0x1c0 [ 27.061976] [] pppol2tp_release+0x1fb/0x2e0 [ 27.067916] [] sock_release+0x96/0x1c0 [ 27.073422] [] sock_close+0x16/0x20 [ 27.078670] [] __fput+0x263/0x700 [ 27.083744] [] ____fput+0x15/0x20 [ 27.088819] [] task_work_run+0x10c/0x180 [ 27.094501] [] do_exit+0x9e1/0x27c0 [ 27.099746] [] ? vm_insert_mixed+0x200/0x200 [ 27.105775] [] ? release_task.part.19+0x1210/0x1210 [ 27.112413] [] ? __do_page_fault+0x5dd/0xd50 [ 27.118441] [] ? up_read+0x1a/0x40 [ 27.123600] [] ? __do_page_fault+0x183/0xd50 [ 27.129627] [] do_group_exit+0x111/0x340 [ 27.135306] [] ? do_group_exit+0x340/0x340 [ 27.141160] [] SyS_exit_group+0x1d/0x20 [ 27.146755] [] do_syscall_64+0x1a6/0x490 [ 27.152437] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 27.159328] [ 27.160934] Allocated by task 5002: [ 27.164537] save_stack_trace+0x16/0x20 [ 27.168481] save_stack+0x43/0xd0 [ 27.171903] kasan_kmalloc+0xc7/0xe0 [ 27.175587] __kmalloc+0x11d/0x300 [ 27.179097] l2tp_session_create+0x38/0x16f0 [ 27.183475] pppol2tp_connect+0x10d7/0x18f0 [ 27.187764] SYSC_connect+0x1b8/0x300 [ 27.191537] SyS_connect+0x24/0x30 [ 27.195047] do_syscall_64+0x1a6/0x490 [ 27.198914] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 27.203992] [ 27.205592] Freed by task 4984: [ 27.208841] save_stack_trace+0x16/0x20 [ 27.212787] save_stack+0x43/0xd0 [ 27.216209] kasan_slab_free+0x72/0xc0 [ 27.220073] kfree+0xfb/0x310 [ 27.223149] l2tp_session_free+0x166/0x200 [ 27.227354] l2tp_tunnel_closeall+0x284/0x350 [ 27.231821] l2tp_udp_encap_destroy+0x87/0xe0 [ 27.236291] udpv6_destroy_sock+0xb1/0xd0 [ 27.240408] sk_common_release+0x6d/0x300 [ 27.244523] udp_lib_close+0x15/0x20 [ 27.248215] inet_release+0xff/0x1d0 [ 27.251898] inet6_release+0x50/0x70 [ 27.255583] sock_release+0x96/0x1c0 [ 27.259266] sock_close+0x16/0x20 [ 27.262693] __fput+0x263/0x700 [ 27.265940] ____fput+0x15/0x20 [ 27.269189] task_work_run+0x10c/0x180 [ 27.273048] do_exit+0x9e1/0x27c0 [ 27.276470] do_group_exit+0x111/0x340 [ 27.280328] SyS_exit_group+0x1d/0x20 [ 27.284099] do_syscall_64+0x1a6/0x490 [ 27.287955] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 27.293024] [ 27.294626] The buggy address belongs to the object at ffff8801c5aea780 [ 27.294626] which belongs to the cache kmalloc-512 of size 512 [ 27.307259] The buggy address is located 0 bytes inside of [ 27.307259] 512-byte region [ffff8801c5aea780, ffff8801c5aea980) [ 27.318928] The buggy address belongs to the page: [ 27.323827] page:ffffea000716ba80 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 27.333999] flags: 0x8000000000004080(slab|head) [ 27.338723] page dumped because: kasan: bad access detected [ 27.344400] [ 27.345994] Memory state around the buggy address: [ 27.350891] ffff8801c5aea680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 27.358219] ffff8801c5aea700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 27.365548] >ffff8801c5aea780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 27.372878] ^ [ 27.376219] ffff8801c5aea800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 27.383548] ffff8801c5aea880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 27.390875] ================================================================== [ 27.398200] Disabling lock debugging due to kernel taint [ 27.403819] Kernel panic - not syncing: panic_on_warn set ... [ 27.403819] [ 27.411165] CPU: 1 PID: 5004 Comm: syz-executor898 Tainted: G B 4.9.100-g73fdfa3 #26 [ 27.420143] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 27.429468] ffff8801d80a7a60 ffffffff81eb0f09 ffffffff843c50e5 00000000ffffffff [ 27.437449] 0000000000000000 0000000000000001 ffffffff8300fbe0 ffff8801d80a7b20 [ 27.445432] ffffffff8141f895 0000000041b58ab3 ffffffff843b87e8 ffffffff8141f6d6 [ 27.453414] Call Trace: [ 27.455977] [] dump_stack+0xc1/0x128 [ 27.461316] [] ? sock_release+0x1c0/0x1c0 [ 27.467086] [] panic+0x1bf/0x3bc [ 27.472073] [] ? add_taint.cold.6+0x16/0x16 [ 27.478016] [] ? ___preempt_schedule+0x16/0x18 [ 27.484218] [] kasan_end_report+0x47/0x4f [ 27.489987] [] kasan_report.cold.6+0x76/0x2fe [ 27.496102] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 27.502827] [] __asan_report_load4_noabort+0x14/0x20 [ 27.509549] [] l2tp_session_queue_purge+0xf4/0x100 [ 27.516101] [] ? sock_release+0x1c0/0x1c0 [ 27.521868] [] pppol2tp_release+0x1fb/0x2e0 [ 27.527810] [] sock_release+0x96/0x1c0 [ 27.533315] [] sock_close+0x16/0x20 [ 27.538563] [] __fput+0x263/0x700 [ 27.543639] [] ____fput+0x15/0x20 [ 27.548732] [] task_work_run+0x10c/0x180 [ 27.554414] [] do_exit+0x9e1/0x27c0 [ 27.559663] [] ? vm_insert_mixed+0x200/0x200 [ 27.565693] [] ? release_task.part.19+0x1210/0x1210 [ 27.572338] [] ? __do_page_fault+0x5dd/0xd50 [ 27.578375] [] ? up_read+0x1a/0x40 [ 27.583549] [] ? __do_page_fault+0x183/0xd50 [ 27.589579] [] do_group_exit+0x111/0x340 [ 27.595262] [] ? do_group_exit+0x340/0x340 [ 27.601120] [] SyS_exit_group+0x1d/0x20 [ 27.606718] [] do_syscall_64+0x1a6/0x490 [ 27.612410] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 27.619794] Dumping ftrace buffer: [ 27.623311] (ftrace buffer empty) [ 27.626994] Kernel Offset: disabled [ 27.630595] Rebooting in 86400 seconds..