[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 12.156244] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 16.879526] random: sshd: uninitialized urandom read (32 bytes read) [ 17.035488] random: sshd: uninitialized urandom read (32 bytes read) [ 17.542749] random: sshd: uninitialized urandom read (32 bytes read) [ 52.367415] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.4' (ECDSA) to the list of known hosts. [ 57.907259] 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 executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program [ 65.785047] ================================================================== [ 65.792426] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 65.799674] Read of size 4 at addr ffff8801c1331400 by task syz-executor547/5202 [ 65.807177] [ 65.808779] CPU: 0 PID: 5202 Comm: syz-executor547 Not tainted 4.9.124-g09eb2ba #35 [ 65.816545] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 65.825878] ffff8801d71e7c98 ffffffff81eb95e9 ffffea000704cc00 ffff8801c1331400 [ 65.833876] 0000000000000000 ffff8801c1331400 0000000000000000 ffff8801d71e7cd0 [ 65.841875] ffffffff8156c35e ffff8801c1331400 0000000000000004 0000000000000000 [ 65.850097] Call Trace: [ 65.852663] [] dump_stack+0xc1/0x128 [ 65.858005] [] print_address_description+0x6c/0x234 [ 65.864645] [] kasan_report.cold.6+0x242/0x2fe [ 65.870850] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 65.877580] [] __asan_report_load4_noabort+0x14/0x20 [ 65.884306] [] l2tp_session_queue_purge+0xf4/0x100 [ 65.890855] [] pppol2tp_release+0x1fb/0x2e0 [ 65.896810] [] __sock_release+0xd7/0x260 [ 65.902498] [] ? __sock_release+0x260/0x260 [ 65.908442] [] sock_close+0x19/0x20 [ 65.913735] [] __fput+0x263/0x700 [ 65.918821] [] ____fput+0x15/0x20 [ 65.923902] [] task_work_run+0x10c/0x180 [ 65.929591] [] exit_to_usermode_loop+0xfc/0x120 [ 65.935889] [] do_fast_syscall_32+0x5c3/0x870 [ 65.942007] [] ? trace_hardirqs_off_thunk+0x1a/0x1c [ 65.948646] [] entry_SYSENTER_compat+0x90/0xa2 [ 65.954911] [ 65.956520] Allocated by task 5203: [ 65.960124] save_stack_trace+0x16/0x20 [ 65.964074] save_stack+0x43/0xd0 [ 65.967499] kasan_kmalloc+0xc7/0xe0 [ 65.971186] __kmalloc+0x11d/0x300 [ 65.974705] l2tp_session_create+0x38/0x16f0 [ 65.979092] pppol2tp_connect+0x10d7/0x18f0 [ 65.983387] SYSC_connect+0x1b8/0x300 [ 65.987161] SyS_connect+0x24/0x30 [ 65.990675] do_fast_syscall_32+0x2f7/0x870 [ 65.994979] entry_SYSENTER_compat+0x90/0xa2 [ 65.999358] [ 66.000964] Freed by task 5186: [ 66.004219] save_stack_trace+0x16/0x20 [ 66.008164] save_stack+0x43/0xd0 [ 66.011590] kasan_slab_free+0x72/0xc0 [ 66.015451] kfree+0xfb/0x310 [ 66.018577] l2tp_session_free+0x166/0x200 [ 66.022792] l2tp_tunnel_closeall+0x284/0x350 [ 66.027260] l2tp_udp_encap_destroy+0x87/0xe0 [ 66.031727] udpv6_destroy_sock+0xb1/0xd0 [ 66.035847] sk_common_release+0x6d/0x300 [ 66.039974] udp_lib_close+0x15/0x20 [ 66.043662] inet_release+0xff/0x1d0 [ 66.047354] inet6_release+0x50/0x70 [ 66.051041] __sock_release+0xd7/0x260 [ 66.054906] sock_close+0x19/0x20 [ 66.058338] __fput+0x263/0x700 [ 66.061591] ____fput+0x15/0x20 [ 66.064845] task_work_run+0x10c/0x180 [ 66.068788] do_exit+0x9e1/0x27b0 [ 66.072221] do_group_exit+0x111/0x340 [ 66.076082] get_signal+0x4cf/0x1450 [ 66.079768] do_signal+0x87/0x19f0 [ 66.083282] exit_to_usermode_loop+0xe1/0x120 [ 66.087747] prepare_exit_to_usermode+0xbb/0xe0 [ 66.092389] retint_user+0x8/0x3c [ 66.095934] [ 66.097558] The buggy address belongs to the object at ffff8801c1331400 [ 66.097558] which belongs to the cache kmalloc-512 of size 512 [ 66.110193] The buggy address is located 0 bytes inside of [ 66.110193] 512-byte region [ffff8801c1331400, ffff8801c1331600) [ 66.121873] The buggy address belongs to the page: [ 66.126786] page:ffffea000704cc00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 66.136974] flags: 0x8000000000004080(slab|head) [ 66.141704] page dumped because: kasan: bad access detected [ 66.147385] [ 66.148991] Memory state around the buggy address: [ 66.153906] ffff8801c1331300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 66.161241] ffff8801c1331380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 66.168574] >ffff8801c1331400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 66.175913] ^ [ 66.179270] ffff8801c1331480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 66.186608] ffff8801c1331500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 66.194053] ================================================================== [ 66.201393] Disabling lock debugging due to kernel taint [ 66.207313] Kernel panic - not syncing: panic_on_warn set ... [ 66.207313] [ 66.214722] CPU: 1 PID: 5202 Comm: syz-executor547 Tainted: G B 4.9.124-g09eb2ba #35 [ 66.223717] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 66.233049] ffff8801d71e7bf8 ffffffff81eb95e9 ffffffff843c828b 00000000ffffffff [ 66.241066] 0000000000000000 0000000000000001 0000000000000000 ffff8801d71e7cb8 [ 66.249089] ffffffff81423eb5 0000000041b58ab3 ffffffff843bb8e8 ffffffff81423cf6 [ 66.257106] Call Trace: [ 66.259677] [] dump_stack+0xc1/0x128 [ 66.265027] [] panic+0x1bf/0x3bc [ 66.270025] [] ? add_taint.cold.6+0x16/0x16 [ 66.275980] [] ? ___preempt_schedule+0x16/0x18 [ 66.282199] [] kasan_end_report+0x47/0x4f [ 66.287978] [] kasan_report.cold.6+0x76/0x2fe [ 66.294106] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 66.300839] [] __asan_report_load4_noabort+0x14/0x20 [ 66.307693] [] l2tp_session_queue_purge+0xf4/0x100 [ 66.314273] [] pppol2tp_release+0x1fb/0x2e0 [ 66.320223] [] __sock_release+0xd7/0x260 [ 66.325915] [] ? __sock_release+0x260/0x260 [ 66.331885] [] sock_close+0x19/0x20 [ 66.337157] [] __fput+0x263/0x700 [ 66.342272] [] ____fput+0x15/0x20 [ 66.347359] [] task_work_run+0x10c/0x180 [ 66.353053] [] exit_to_usermode_loop+0xfc/0x120 [ 66.359348] [] do_fast_syscall_32+0x5c3/0x870 [ 66.365470] [] ? trace_hardirqs_off_thunk+0x1a/0x1c [ 66.372122] [] entry_SYSENTER_compat+0x90/0xa2 [ 66.378664] Dumping ftrace buffer: [ 66.382191] (ftrace buffer empty) [ 66.385881] Kernel Offset: disabled [ 66.389487] Rebooting in 86400 seconds..