[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 15.666586] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. [ 16.308006] random: sshd: uninitialized urandom read (32 bytes read) [ 16.543635] random: sshd: uninitialized urandom read (32 bytes read) Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 17.694848] random: sshd: uninitialized urandom read (32 bytes read) [ 17.848665] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.8' (ECDSA) to the list of known hosts. [ 23.237393] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 23.429982] ================================================================== [ 23.437385] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 23.444631] Read of size 4 at addr ffff8801b7f93180 by task syz-executor952/3789 [ 23.452132] [ 23.453734] CPU: 0 PID: 3789 Comm: syz-executor952 Not tainted 4.9.105-gd7e64f8 #43 [ 23.461494] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 23.470832] ffff8801beff7cb0 ffffffff81eb41a9 ffffea0006dfe480 ffff8801b7f93180 [ 23.478811] 0000000000000000 ffff8801b7f93180 ffffffff83013be0 ffff8801beff7ce8 [ 23.486794] ffffffff81567e49 ffff8801b7f93180 0000000000000004 0000000000000000 [ 23.494768] Call Trace: [ 23.497335] [] dump_stack+0xc1/0x128 [ 23.502671] [] ? sock_release+0x1c0/0x1c0 [ 23.508441] [] print_address_description+0x6c/0x234 [ 23.515081] [] ? sock_release+0x1c0/0x1c0 [ 23.520853] [] kasan_report.cold.6+0x242/0x2fe [ 23.527059] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 23.533785] [] __asan_report_load4_noabort+0x14/0x20 [ 23.540512] [] l2tp_session_queue_purge+0xf4/0x100 [ 23.547061] [] ? sock_release+0x1c0/0x1c0 [ 23.552830] [] pppol2tp_release+0x1fb/0x2e0 [ 23.558774] [] sock_release+0x96/0x1c0 [ 23.564305] [] sock_close+0x16/0x20 [ 23.569553] [] __fput+0x263/0x700 [ 23.574639] [] ____fput+0x15/0x20 [ 23.579723] [] task_work_run+0x10c/0x180 [ 23.585405] [] exit_to_usermode_loop+0xfc/0x120 [ 23.591695] [] do_syscall_64+0x364/0x490 [ 23.597380] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 23.604273] [ 23.605873] Allocated by task 3788: [ 23.609483] save_stack_trace+0x16/0x20 [ 23.613430] save_stack+0x43/0xd0 [ 23.616853] kasan_kmalloc+0xc7/0xe0 [ 23.620537] __kmalloc+0x11d/0x300 [ 23.624047] l2tp_session_create+0x38/0x16f0 [ 23.628424] pppol2tp_connect+0x10d7/0x18f0 [ 23.632726] SYSC_connect+0x1b8/0x300 [ 23.636498] SyS_connect+0x24/0x30 [ 23.640010] do_syscall_64+0x1a6/0x490 [ 23.643869] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 23.648937] [ 23.650537] Freed by task 3788: [ 23.653799] save_stack_trace+0x16/0x20 [ 23.657741] save_stack+0x43/0xd0 [ 23.661175] kasan_slab_free+0x72/0xc0 [ 23.665042] kfree+0xfb/0x310 [ 23.668119] l2tp_session_free+0x166/0x200 [ 23.672324] l2tp_tunnel_closeall+0x284/0x350 [ 23.676796] l2tp_udp_encap_destroy+0x87/0xe0 [ 23.681263] udp_destroy_sock+0x118/0x1a0 [ 23.686606] sk_common_release+0x6d/0x300 [ 23.690723] udp_lib_close+0x15/0x20 [ 23.694409] inet_release+0xff/0x1d0 [ 23.698095] sock_release+0x96/0x1c0 [ 23.701807] sock_close+0x16/0x20 [ 23.705234] __fput+0x263/0x700 [ 23.708571] ____fput+0x15/0x20 [ 23.711835] task_work_run+0x10c/0x180 [ 23.715693] exit_to_usermode_loop+0xfc/0x120 [ 23.720157] do_syscall_64+0x364/0x490 [ 23.724016] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 23.729087] [ 23.730687] The buggy address belongs to the object at ffff8801b7f93180 [ 23.730687] which belongs to the cache kmalloc-512 of size 512 [ 23.743312] The buggy address is located 0 bytes inside of [ 23.743312] 512-byte region [ffff8801b7f93180, ffff8801b7f93380) [ 23.754990] The buggy address belongs to the page: [ 23.759891] page:ffffea0006dfe480 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 23.770081] flags: 0x8000000000004080(slab|head) [ 23.774804] page dumped because: kasan: bad access detected [ 23.780481] [ 23.782080] Memory state around the buggy address: [ 23.786978] ffff8801b7f93080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 23.794316] ffff8801b7f93100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 23.801645] >ffff8801b7f93180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 23.808974] ^ [ 23.812318] ffff8801b7f93200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 23.819658] ffff8801b7f93280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 23.827000] ================================================================== [ 23.834338] Disabling lock debugging due to kernel taint [ 23.839899] Kernel panic - not syncing: panic_on_warn set ... [ 23.839899] [ 23.847262] CPU: 0 PID: 3789 Comm: syz-executor952 Tainted: G B 4.9.105-gd7e64f8 #43 [ 23.856250] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 23.865595] ffff8801beff7c10 ffffffff81eb41a9 ffffffff843c625d 00000000ffffffff [ 23.873581] 0000000000000000 0000000000000000 ffffffff83013be0 ffff8801beff7cd0 [ 23.881571] ffffffff81421e15 0000000041b58ab3 ffffffff843b9990 ffffffff81421c56 [ 23.889557] Call Trace: [ 23.892123] [] dump_stack+0xc1/0x128 [ 23.897462] [] ? sock_release+0x1c0/0x1c0 [ 23.903234] [] panic+0x1bf/0x3bc [ 23.908221] [] ? add_taint.cold.6+0x16/0x16 [ 23.914177] [] ? ___preempt_schedule+0x16/0x18 [ 23.920381] [] kasan_end_report+0x47/0x4f [ 23.926148] [] kasan_report.cold.6+0x76/0x2fe [ 23.932268] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 23.938992] [] __asan_report_load4_noabort+0x14/0x20 [ 23.945723] [] l2tp_session_queue_purge+0xf4/0x100 [ 23.952274] [] ? sock_release+0x1c0/0x1c0 [ 23.958043] [] pppol2tp_release+0x1fb/0x2e0 [ 23.964001] [] sock_release+0x96/0x1c0 [ 23.969512] [] sock_close+0x16/0x20 [ 23.974783] [] __fput+0x263/0x700 [ 23.979859] [] ____fput+0x15/0x20 [ 23.984940] [] task_work_run+0x10c/0x180 [ 23.990632] [] exit_to_usermode_loop+0xfc/0x120 [ 23.996923] [] do_syscall_64+0x364/0x490 [ 24.002605] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 24.009982] Dumping ftrace buffer: [ 24.013495] (ftrace buffer empty) [ 24.017177] Kernel Offset: disabled [ 24.020788] Rebooting in 86400 seconds..