[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 16.078732] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 21.022322] random: sshd: uninitialized urandom read (32 bytes read) [ 21.453002] random: sshd: uninitialized urandom read (32 bytes read) [ 22.267196] random: sshd: uninitialized urandom read (32 bytes read) [ 74.691959] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.43' (ECDSA) to the list of known hosts. [ 80.333552] 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 [ 80.763175] ================================================================== [ 80.770556] BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xed/0x110 [ 80.777983] Read of size 4 at addr ffff8801b88baf00 by task syz-executor205/3833 [ 80.785708] [ 80.787319] CPU: 0 PID: 3833 Comm: syz-executor205 Not tainted 4.9.110-g00a0bcb #4 [ 80.795002] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 80.804352] ffff8801d884fc30 ffffffff81eb2329 ffffea0006e22e80 ffff8801b88baf00 [ 80.812362] 0000000000000000 ffff8801b88baf00 ffffffff83011be0 ffff8801d884fc68 [ 80.820367] ffffffff81567a89 ffff8801b88baf00 0000000000000004 0000000000000000 [ 80.828449] Call Trace: [ 80.831116] [] dump_stack+0xc1/0x128 [ 80.836454] [] ? sock_release+0x1c0/0x1c0 [ 80.842237] [] print_address_description+0x6c/0x234 [ 80.848878] [] ? sock_release+0x1c0/0x1c0 [ 80.855008] [] kasan_report.cold.6+0x242/0x2fe [ 80.861316] [] ? pppol2tp_session_destruct+0xed/0x110 [ 80.868139] [] __asan_report_load4_noabort+0x14/0x20 [ 80.874872] [] pppol2tp_session_destruct+0xed/0x110 [ 80.881703] [] ? pppol2tp_seq_start+0x4e0/0x4e0 [ 80.888001] [] __sk_destruct+0x55/0x590 [ 80.893608] [] ? sock_release+0x1c0/0x1c0 [ 80.899382] [] sk_destruct+0x63/0x80 [ 80.904735] [] __sk_free+0x4f/0x220 [ 80.910679] [] sk_free+0x2b/0x40 [ 80.915931] [] pppol2tp_release+0x239/0x2e0 [ 80.921966] [] sock_release+0x96/0x1c0 [ 80.927479] [] sock_close+0x16/0x20 [ 80.932738] [] __fput+0x263/0x700 [ 80.937816] [] ____fput+0x15/0x20 [ 80.942905] [] task_work_run+0x10c/0x180 [ 80.948767] [] exit_to_usermode_loop+0xfc/0x120 [ 80.955060] [] do_syscall_64+0x364/0x490 [ 80.960753] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 80.967690] [ 80.969308] Allocated by task 3833: [ 80.972926] save_stack_trace+0x16/0x20 [ 80.976875] save_stack+0x43/0xd0 [ 80.980388] kasan_kmalloc+0xc7/0xe0 [ 80.984340] __kmalloc+0x11d/0x300 [ 80.987856] l2tp_session_create+0x38/0x16f0 [ 80.992237] pppol2tp_connect+0x10d7/0x18f0 [ 80.996537] SYSC_connect+0x1b8/0x300 [ 81.000314] SyS_connect+0x24/0x30 [ 81.003833] do_syscall_64+0x1a6/0x490 [ 81.007706] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 81.012953] [ 81.014563] Freed by task 3832: [ 81.017819] save_stack_trace+0x16/0x20 [ 81.021777] save_stack+0x43/0xd0 [ 81.025215] kasan_slab_free+0x72/0xc0 [ 81.029089] kfree+0xfb/0x310 [ 81.032174] l2tp_session_free+0x166/0x200 [ 81.036383] l2tp_tunnel_closeall+0x284/0x350 [ 81.040864] l2tp_udp_encap_destroy+0x87/0xe0 [ 81.045335] udpv6_destroy_sock+0xb1/0xd0 [ 81.049462] sk_common_release+0x6d/0x300 [ 81.053585] udp_lib_close+0x15/0x20 [ 81.057282] inet_release+0xff/0x1d0 [ 81.060971] inet6_release+0x50/0x70 [ 81.064770] sock_release+0x96/0x1c0 [ 81.068474] sock_close+0x16/0x20 [ 81.071902] __fput+0x263/0x700 [ 81.075155] ____fput+0x15/0x20 [ 81.078464] task_work_run+0x10c/0x180 [ 81.082484] exit_to_usermode_loop+0xfc/0x120 [ 81.087043] do_syscall_64+0x364/0x490 [ 81.090911] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 81.095985] [ 81.097592] The buggy address belongs to the object at ffff8801b88baf00 [ 81.097592] which belongs to the cache kmalloc-512 of size 512 [ 81.110222] The buggy address is located 0 bytes inside of [ 81.110222] 512-byte region [ffff8801b88baf00, ffff8801b88bb100) [ 81.121982] The buggy address belongs to the page: [ 81.126897] page:ffffea0006e22e80 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 81.137094] flags: 0x8000000000004080(slab|head) [ 81.141824] page dumped because: kasan: bad access detected [ 81.147503] [ 81.149292] Memory state around the buggy address: [ 81.154216] ffff8801b88bae00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 81.161559] ffff8801b88bae80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 81.168896] >ffff8801b88baf00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 81.176315] ^ [ 81.179656] ffff8801b88baf80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 81.187184] ffff8801b88bb000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 81.194515] ================================================================== [ 81.201863] Disabling lock debugging due to kernel taint [ 81.207762] Kernel panic - not syncing: panic_on_warn set ... [ 81.207762] executing program [ 81.215128] CPU: 0 PID: 3833 Comm: syz-executor205 Tainted: G B 4.9.110-g00a0bcb #4 [ 81.224040] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 81.233377] ffff8801d884fb90 ffffffff81eb2329 ffffffff843c7167 00000000ffffffff [ 81.241433] 0000000000000000 0000000000000000 ffffffff83011be0 ffff8801d884fc50 [ 81.249450] ffffffff81421925 0000000041b58ab3 ffffffff843ba880 ffffffff81421766 [ 81.257506] Call Trace: [ 81.260075] [] dump_stack+0xc1/0x128 [ 81.265433] [] ? sock_release+0x1c0/0x1c0 [ 81.271312] [] panic+0x1bf/0x3bc [ 81.276313] [] ? add_taint.cold.6+0x16/0x16 [ 81.282271] [] ? ___preempt_schedule+0x16/0x18 [ 81.288507] [] kasan_end_report+0x47/0x4f [ 81.294382] [] kasan_report.cold.6+0x76/0x2fe [ 81.300593] [] ? pppol2tp_session_destruct+0xed/0x110 [ 81.307522] [] __asan_report_load4_noabort+0x14/0x20 [ 81.314266] [] pppol2tp_session_destruct+0xed/0x110 [ 81.320916] [] ? pppol2tp_seq_start+0x4e0/0x4e0 [ 81.327299] [] __sk_destruct+0x55/0x590 [ 81.332899] [] ? sock_release+0x1c0/0x1c0 [ 81.338759] [] sk_destruct+0x63/0x80 [ 81.344100] [] __sk_free+0x4f/0x220 [ 81.349366] [] sk_free+0x2b/0x40 [ 81.354358] [] pppol2tp_release+0x239/0x2e0 [ 81.360318] [] sock_release+0x96/0x1c0 [ 81.365833] [] sock_close+0x16/0x20 [ 81.371089] [] __fput+0x263/0x700 [ 81.376168] [] ____fput+0x15/0x20 [ 81.381248] [] task_work_run+0x10c/0x180 [ 81.387024] [] exit_to_usermode_loop+0xfc/0x120 [ 81.393329] [] do_syscall_64+0x364/0x490 [ 81.399016] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 81.406286] Dumping ftrace buffer: [ 81.409843] (ftrace buffer empty) [ 81.413529] Kernel Offset: disabled [ 81.417221] Rebooting in 86400 seconds..