[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 13.605666] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 17.261336] random: sshd: uninitialized urandom read (32 bytes read) [ 17.674642] random: sshd: uninitialized urandom read (32 bytes read) [ 18.546683] random: sshd: uninitialized urandom read (32 bytes read) [ 22.859753] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.21' (ECDSA) to the list of known hosts. [ 28.257495] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 28.399135] ================================================================== [ 28.406527] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 28.413777] Read of size 4 at addr ffff8801b5aea500 by task syz-executor562/3808 [ 28.421279] [ 28.422884] CPU: 0 PID: 3808 Comm: syz-executor562 Not tainted 4.9.111-g03c70fe #6 [ 28.430567] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 28.439895] ffff8801c4827cb0 ffffffff81eb2729 ffffea0006d6ba80 ffff8801b5aea500 [ 28.447910] 0000000000000000 ffff8801b5aea500 ffffffff83012be0 ffff8801c4827ce8 [ 28.455936] ffffffff81567b59 ffff8801b5aea500 0000000000000004 0000000000000000 [ 28.463922] Call Trace: [ 28.466538] [] dump_stack+0xc1/0x128 [ 28.471883] [] ? sock_release+0x1c0/0x1c0 [ 28.477656] [] print_address_description+0x6c/0x234 [ 28.484310] [] ? sock_release+0x1c0/0x1c0 [ 28.490082] [] kasan_report.cold.6+0x242/0x2fe [ 28.496290] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 28.503020] [] __asan_report_load4_noabort+0x14/0x20 [ 28.509747] [] l2tp_session_queue_purge+0xf4/0x100 [ 28.516308] [] ? sock_release+0x1c0/0x1c0 [ 28.522089] [] pppol2tp_release+0x1fb/0x2e0 [ 28.528036] [] sock_release+0x96/0x1c0 [ 28.533547] [] sock_close+0x16/0x20 [ 28.538800] [] __fput+0x263/0x700 [ 28.543880] [] ____fput+0x15/0x20 [ 28.548966] [] task_work_run+0x10c/0x180 [ 28.554651] [] exit_to_usermode_loop+0xfc/0x120 [ 28.560950] [] do_syscall_64+0x364/0x490 [ 28.566638] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.573535] [ 28.575135] Allocated by task 3807: [ 28.578738] save_stack_trace+0x16/0x20 [ 28.582689] save_stack+0x43/0xd0 [ 28.586114] kasan_kmalloc+0xc7/0xe0 [ 28.589797] __kmalloc+0x11d/0x300 [ 28.593324] l2tp_session_create+0x38/0x16f0 [ 28.597718] pppol2tp_connect+0x10d7/0x18f0 [ 28.602017] SYSC_connect+0x1b8/0x300 [ 28.605790] SyS_connect+0x24/0x30 [ 28.609304] do_syscall_64+0x1a6/0x490 [ 28.613175] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.618263] [ 28.619865] Freed by task 3807: [ 28.623127] save_stack_trace+0x16/0x20 [ 28.627074] save_stack+0x43/0xd0 [ 28.630498] kasan_slab_free+0x72/0xc0 [ 28.634356] kfree+0xfb/0x310 [ 28.637433] l2tp_session_free+0x166/0x200 [ 28.641653] l2tp_tunnel_closeall+0x284/0x350 [ 28.646121] l2tp_udp_encap_destroy+0x87/0xe0 [ 28.650588] udp_destroy_sock+0x118/0x1a0 [ 28.654707] sk_common_release+0x6d/0x300 [ 28.658838] udp_lib_close+0x15/0x20 [ 28.662526] inet_release+0xff/0x1d0 [ 28.666214] sock_release+0x96/0x1c0 [ 28.669897] sock_close+0x16/0x20 [ 28.673335] __fput+0x263/0x700 [ 28.676597] ____fput+0x15/0x20 [ 28.679850] task_work_run+0x10c/0x180 [ 28.683717] exit_to_usermode_loop+0xfc/0x120 [ 28.688192] do_syscall_64+0x364/0x490 [ 28.692063] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.697136] [ 28.698736] The buggy address belongs to the object at ffff8801b5aea500 [ 28.698736] which belongs to the cache kmalloc-512 of size 512 [ 28.711366] The buggy address is located 0 bytes inside of [ 28.711366] 512-byte region [ffff8801b5aea500, ffff8801b5aea700) [ 28.723058] The buggy address belongs to the page: [ 28.727968] page:ffffea0006d6ba80 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 28.738158] flags: 0x8000000000004080(slab|head) [ 28.742880] page dumped because: kasan: bad access detected [ 28.748556] [ 28.750173] Memory state around the buggy address: [ 28.755073] ffff8801b5aea400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.762504] ffff8801b5aea480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 28.769846] >ffff8801b5aea500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.777185] ^ [ 28.780535] ffff8801b5aea580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.787866] ffff8801b5aea600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 28.795192] ================================================================== [ 28.802521] Disabling lock debugging due to kernel taint [ 28.808278] Kernel panic - not syncing: panic_on_warn set ... [ 28.808278] [ 28.815622] CPU: 0 PID: 3808 Comm: syz-executor562 Tainted: G B 4.9.111-g03c70fe #6 [ 28.824515] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 28.833929] ffff8801c4827c10 ffffffff81eb2729 ffffffff843c71a7 00000000ffffffff [ 28.841908] 0000000000000000 0000000000000000 ffffffff83012be0 ffff8801c4827cd0 [ 28.849889] ffffffff814219f5 0000000041b58ab3 ffffffff843ba8c0 ffffffff81421836 [ 28.857904] Call Trace: [ 28.860465] [] dump_stack+0xc1/0x128 [ 28.865801] [] ? sock_release+0x1c0/0x1c0 [ 28.871572] [] panic+0x1bf/0x3bc [ 28.876570] [] ? add_taint.cold.6+0x16/0x16 [ 28.882513] [] ? ___preempt_schedule+0x16/0x18 [ 28.888734] [] kasan_end_report+0x47/0x4f [ 28.894512] [] kasan_report.cold.6+0x76/0x2fe [ 28.900630] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 28.907355] [] __asan_report_load4_noabort+0x14/0x20 [ 28.914079] [] l2tp_session_queue_purge+0xf4/0x100 [ 28.920639] [] ? sock_release+0x1c0/0x1c0 [ 28.926414] [] pppol2tp_release+0x1fb/0x2e0 [ 28.932356] [] sock_release+0x96/0x1c0 [ 28.937864] [] sock_close+0x16/0x20 [ 28.943116] [] __fput+0x263/0x700 [ 28.948188] [] ____fput+0x15/0x20 [ 28.953266] [] task_work_run+0x10c/0x180 [ 28.958958] [] exit_to_usermode_loop+0xfc/0x120 [ 28.965248] [] do_syscall_64+0x364/0x490 [ 28.970940] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.978248] Dumping ftrace buffer: [ 28.981761] (ftrace buffer empty) [ 28.985455] Kernel Offset: disabled [ 28.989071] Rebooting in 86400 seconds..