[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 12.929092] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. [ 13.714880] random: sshd: uninitialized urandom read (32 bytes read) Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 14.161368] random: sshd: uninitialized urandom read (32 bytes read) [ 14.860152] random: sshd: uninitialized urandom read (32 bytes read) [ 15.003958] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.2' (ECDSA) to the list of known hosts. [ 20.405753] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 20.557471] ================================================================== [ 20.564858] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 20.572107] Read of size 4 at addr ffff8801caf60f00 by task syz-executor920/3791 [ 20.579607] [ 20.581208] CPU: 0 PID: 3791 Comm: syz-executor920 Not tainted 4.9.105-gd7e64f8 #40 [ 20.588969] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 20.598296] ffff8801b681fcb0 ffffffff81eb41a9 ffffea00072bd800 ffff8801caf60f00 [ 20.606286] 0000000000000000 ffff8801caf60f00 ffffffff83013be0 ffff8801b681fce8 [ 20.614252] ffffffff81567e49 ffff8801caf60f00 0000000000000004 0000000000000000 [ 20.622315] Call Trace: [ 20.624876] [] dump_stack+0xc1/0x128 [ 20.630210] [] ? sock_release+0x1c0/0x1c0 [ 20.635978] [] print_address_description+0x6c/0x234 [ 20.642614] [] ? sock_release+0x1c0/0x1c0 [ 20.648383] [] kasan_report.cold.6+0x242/0x2fe [ 20.654592] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 20.661316] [] __asan_report_load4_noabort+0x14/0x20 [ 20.668038] [] l2tp_session_queue_purge+0xf4/0x100 [ 20.674588] [] ? sock_release+0x1c0/0x1c0 [ 20.680361] [] pppol2tp_release+0x1fb/0x2e0 [ 20.686301] [] sock_release+0x96/0x1c0 [ 20.691820] [] sock_close+0x16/0x20 [ 20.697083] [] __fput+0x263/0x700 [ 20.702158] [] ____fput+0x15/0x20 [ 20.707232] [] task_work_run+0x10c/0x180 [ 20.712912] [] exit_to_usermode_loop+0xfc/0x120 [ 20.719200] [] do_syscall_64+0x364/0x490 [ 20.724879] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 20.731782] [ 20.733380] Allocated by task 3790: [ 20.736978] save_stack_trace+0x16/0x20 [ 20.740924] save_stack+0x43/0xd0 [ 20.744343] kasan_kmalloc+0xc7/0xe0 [ 20.748024] __kmalloc+0x11d/0x300 [ 20.751536] l2tp_session_create+0x38/0x16f0 [ 20.755914] pppol2tp_connect+0x10d7/0x18f0 [ 20.760212] SYSC_connect+0x1b8/0x300 [ 20.763989] SyS_connect+0x24/0x30 [ 20.767498] do_syscall_64+0x1a6/0x490 [ 20.771353] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 20.776439] [ 20.778047] Freed by task 3790: [ 20.781301] save_stack_trace+0x16/0x20 [ 20.785243] save_stack+0x43/0xd0 [ 20.788664] kasan_slab_free+0x72/0xc0 [ 20.792518] kfree+0xfb/0x310 [ 20.795593] l2tp_session_free+0x166/0x200 [ 20.799796] l2tp_tunnel_closeall+0x284/0x350 [ 20.804258] l2tp_udp_encap_destroy+0x87/0xe0 [ 20.808723] udp_destroy_sock+0x118/0x1a0 [ 20.812843] sk_common_release+0x6d/0x300 [ 20.816960] udp_lib_close+0x15/0x20 [ 20.820646] inet_release+0xff/0x1d0 [ 20.824329] sock_release+0x96/0x1c0 [ 20.828021] sock_close+0x16/0x20 [ 20.831446] __fput+0x263/0x700 [ 20.834694] ____fput+0x15/0x20 [ 20.837950] task_work_run+0x10c/0x180 [ 20.841806] exit_to_usermode_loop+0xfc/0x120 [ 20.846272] do_syscall_64+0x364/0x490 [ 20.850127] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 20.855193] [ 20.856791] The buggy address belongs to the object at ffff8801caf60f00 [ 20.856791] which belongs to the cache kmalloc-512 of size 512 [ 20.869415] The buggy address is located 0 bytes inside of [ 20.869415] 512-byte region [ffff8801caf60f00, ffff8801caf61100) [ 20.881082] The buggy address belongs to the page: [ 20.885983] page:ffffea00072bd800 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 20.896161] flags: 0x8000000000004080(slab|head) [ 20.900883] page dumped because: kasan: bad access detected [ 20.906557] [ 20.908156] Memory state around the buggy address: [ 20.913055] ffff8801caf60e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 20.920389] ffff8801caf60e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 20.927718] >ffff8801caf60f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 20.935052] ^ [ 20.938392] ffff8801caf60f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 20.945721] ffff8801caf61000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 20.953046] ================================================================== [ 20.960372] Disabling lock debugging due to kernel taint [ 20.965902] Kernel panic - not syncing: panic_on_warn set ... [ 20.965902] [ 20.973248] CPU: 0 PID: 3791 Comm: syz-executor920 Tainted: G B 4.9.105-gd7e64f8 #40 [ 20.982224] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 20.991550] ffff8801b681fc10 ffffffff81eb41a9 ffffffff843c625d 00000000ffffffff [ 20.999542] 0000000000000000 0000000000000000 ffffffff83013be0 ffff8801b681fcd0 [ 21.007512] ffffffff81421e15 0000000041b58ab3 ffffffff843b9990 ffffffff81421c56 [ 21.015483] Call Trace: [ 21.018043] [] dump_stack+0xc1/0x128 [ 21.023376] [] ? sock_release+0x1c0/0x1c0 [ 21.029142] [] panic+0x1bf/0x3bc [ 21.034130] [] ? add_taint.cold.6+0x16/0x16 [ 21.040075] [] ? ___preempt_schedule+0x16/0x18 [ 21.046282] [] kasan_end_report+0x47/0x4f [ 21.052058] [] kasan_report.cold.6+0x76/0x2fe [ 21.058174] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 21.064895] [] __asan_report_load4_noabort+0x14/0x20 [ 21.071618] [] l2tp_session_queue_purge+0xf4/0x100 [ 21.078168] [] ? sock_release+0x1c0/0x1c0 [ 21.083940] [] pppol2tp_release+0x1fb/0x2e0 [ 21.089886] [] sock_release+0x96/0x1c0 [ 21.095390] [] sock_close+0x16/0x20 [ 21.100637] [] __fput+0x263/0x700 [ 21.105711] [] ____fput+0x15/0x20 [ 21.110788] [] task_work_run+0x10c/0x180 [ 21.116470] [] exit_to_usermode_loop+0xfc/0x120 [ 21.122765] [] do_syscall_64+0x364/0x490 [ 21.128446] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 21.135858] Dumping ftrace buffer: [ 21.139376] (ftrace buffer empty) [ 21.143054] Kernel Offset: disabled [ 21.146653] Rebooting in 86400 seconds..