[....] Starting file context maintaining daemon: restorecond[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 16.497837] random: sshd: uninitialized urandom read (32 bytes read, 32 bits of entropy available) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 20.634170] random: sshd: uninitialized urandom read (32 bytes read, 36 bits of entropy available) [ 20.846839] random: sshd: uninitialized urandom read (32 bytes read, 36 bits of entropy available) [ 21.663143] random: sshd: uninitialized urandom read (32 bytes read, 88 bits of entropy available) [ 21.848201] random: sshd: uninitialized urandom read (32 bytes read, 95 bits of entropy available) Warning: Permanently added '10.128.15.208' (ECDSA) to the list of known hosts. [ 27.226349] random: sshd: uninitialized urandom read (32 bytes read, 102 bits of entropy available) executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program [ 28.201747] ================================================================== [ 28.209161] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xe8/0x100 [ 28.216408] Read of size 4 at addr ffff8800b4bf9900 by task syzkaller123327/3859 [ 28.223908] [ 28.225517] CPU: 0 PID: 3859 Comm: syzkaller123327 Not tainted 4.4.112-g52c02cf #30 [ 28.233280] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 28.242606] 0000000000000000 fc69e61071f95133 ffff8801cf8d77f8 ffffffff81d056fd [ 28.250589] ffffea0002d2fe00 ffff8800b4bf9900 0000000000000000 ffff8800b4bf9900 [ 28.258562] ffffffff82dea6e0 ffff8801cf8d7830 ffffffff814fd953 ffff8800b4bf9900 [ 28.266541] Call Trace: [ 28.269104] [] dump_stack+0xc1/0x124 [ 28.274441] [] ? sock_release+0x1e0/0x1e0 [ 28.280214] [] print_address_description+0x73/0x260 [ 28.286849] [] ? sock_release+0x1e0/0x1e0 [ 28.292655] [] kasan_report+0x285/0x370 [ 28.298250] [] ? l2tp_session_queue_purge+0xe8/0x100 [ 28.304973] [] __asan_report_load4_noabort+0x14/0x20 [ 28.311695] [] l2tp_session_queue_purge+0xe8/0x100 [ 28.318245] [] ? sock_release+0x1e0/0x1e0 [ 28.324017] [] pppol2tp_release+0x1ff/0x310 [ 28.329958] [] sock_release+0x8d/0x1e0 [ 28.335468] [] sock_close+0x16/0x20 [ 28.340714] [] __fput+0x233/0x6d0 [ 28.345786] [] ____fput+0x15/0x20 [ 28.350863] [] task_work_run+0x104/0x180 [ 28.356548] [] do_exit+0x871/0x2a20 [ 28.361800] [] ? __lock_is_held+0xa1/0xf0 [ 28.367574] [] ? rcu_read_lock_sched_held+0x103/0x120 [ 28.374395] [] ? release_task+0x1240/0x1240 [ 28.380340] [] do_group_exit+0x108/0x320 [ 28.386023] [] get_signal+0x565/0x1660 [ 28.391536] [] do_signal+0x8b/0x1d40 [ 28.396870] [] ? spurious_fault+0x370/0x370 [ 28.402812] [] ? setup_sigcontext+0x780/0x780 [ 28.408942] [] ? __lock_is_held+0xa1/0xf0 [ 28.414709] [] ? __bad_area_nosemaphore+0x220/0x420 [ 28.421344] [] ? bad_area+0x53/0x80 [ 28.426592] [] ? exit_to_usermode_loop+0xec/0x170 [ 28.433055] [] exit_to_usermode_loop+0x122/0x170 [ 28.439431] [] prepare_exit_to_usermode+0xe3/0x100 [ 28.445983] [] retint_user+0x8/0x3c [ 28.451226] [ 28.452825] Allocated by task 3858: [ 28.456419] [] save_stack_trace+0x26/0x50 [ 28.462308] [] save_stack+0x43/0xd0 [ 28.467677] [] kasan_kmalloc+0xad/0xe0 [ 28.473308] [] __kmalloc+0x124/0x320 [ 28.478768] [] l2tp_session_create+0x39/0x10f0 [ 28.485089] [] pppol2tp_connect+0x10fc/0x1930 [ 28.491324] [] SYSC_connect+0x1b6/0x310 [ 28.497036] [] SyS_connect+0x24/0x30 [ 28.502491] [] entry_SYSCALL_64_fastpath+0x16/0x92 [ 28.509164] [ 28.510764] Freed by task 3829: [ 28.514010] [] save_stack_trace+0x26/0x50 [ 28.519900] [] save_stack+0x43/0xd0 [ 28.525266] [] kasan_slab_free+0x72/0xc0 [ 28.531065] [] kfree+0xfc/0x300 [ 28.536084] [] l2tp_session_free+0x170/0x200 [ 28.542226] [] l2tp_tunnel_closeall+0x2d1/0x3b0 [ 28.548632] [] l2tp_udp_encap_destroy+0x8b/0xf0 [ 28.555039] [] udpv6_destroy_sock+0xb1/0xd0 [ 28.561097] [] sk_common_release+0x6b/0x300 [ 28.567155] [] udp_lib_close+0x15/0x20 [ 28.572793] [] inet_release+0xfa/0x1d0 [ 28.578417] [] inet6_release+0x50/0x70 [ 28.584045] [] sock_release+0x8d/0x1e0 [ 28.589672] [] sock_close+0x16/0x20 [ 28.595037] [] __fput+0x233/0x6d0 [ 28.600229] [] ____fput+0x15/0x20 [ 28.605422] [] task_work_run+0x104/0x180 [ 28.611227] [] do_exit+0x871/0x2a20 [ 28.616596] [] do_group_exit+0x108/0x320 [ 28.622394] [] get_signal+0x565/0x1660 [ 28.628020] [] do_signal+0x8b/0x1d40 [ 28.633476] [] exit_to_usermode_loop+0x122/0x170 [ 28.639970] [] prepare_exit_to_usermode+0xe3/0x100 [ 28.646639] [] retint_user+0x8/0x3c [ 28.652007] [ 28.653606] The buggy address belongs to the object at ffff8800b4bf9900 [ 28.653606] which belongs to the cache kmalloc-512 of size 512 [ 28.666230] The buggy address is located 0 bytes inside of [ 28.666230] 512-byte region [ffff8800b4bf9900, ffff8800b4bf9b00) [ 28.677903] The buggy address belongs to the page: [ 30.340833] PANIC: double fault, error_code: 0x0 [ 30.345625] CPU: 0 PID: 3859 Comm: syzkaller123327 Not tainted 4.4.112-g52c02cf #30 [ 30.353389] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 30.362714] task: ffff8801d0758000 task.stack: ffff8801cf8d0000 [ 30.368741] RIP: 0010:[] [] dump_page_badflags+0xd/0x250 [ 30.377505] RSP: 0018:ffff880100000000 EFLAGS: 00010046 [ 30.382923] RAX: ffff8801d0758000 RBX: ffffea0002d2fe00 RCX: ffffffff8148fea0 [ 30.390168] RDX: 0000000000000000 RSI: ffffffff838a8620 RDI: ffffea0002d2fe00 [ 30.397409] RBP: ffff880100000018 R08: 0000000000000001 R09: 0000000000000000 [ 30.404654] R10: 0000000000000002 R11: fffffbfff0ad7a1e R12: 0000000000000000 [ 30.411910] R13: ffffffff838a8620 R14: 0000000000000000 R15: 0000000000000000 [ 30.419165] FS: 0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000 [ 30.427364] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 30.433217] CR2: ffff8800fffffff8 CR3: 00000000b3cf4000 CR4: 0000000000160670 [ 30.440466] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 30.447707] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 30.454948] Stack: [ 30.457064] [ 30.458659] Call Trace: [ 30.461210] [ 30.463240] Code: ff e8 a8 e2 06 00 e9 50 fd ff ff e8 9e e2 06 00 e9 1d fd ff ff 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 57 41 56 41 55 49 89 f5 <41> 54 49 89 d4 53 48 89 fb 48 83 ec 08 e8 11 01 ed ff 48 8d 7b [ 30.490303] Kernel panic - not syncing: Machine halted. [ 30.495640] CPU: 0 PID: 3859 Comm: syzkaller123327 Not tainted 4.4.112-g52c02cf #30 [ 30.503408] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 30.512733] 0000000000000000 fc69e61071f95133 ffff8801db20ce38 ffffffff81d056fd [ 30.520700] ffffffff83836a60 ffff8801db20cf10 ffffffff83808040 ffff880100000000 [ 30.528661] 0000000000000000 ffff8801db20cf00 ffffffff81419dca 0000000041b58ab3 [ 30.536627] Call Trace: [ 30.539177] <#DF> [] dump_stack+0xc1/0x124 [ 30.545245] [] panic+0x1aa/0x388 [ 30.550230] [] ? percpu_up_read.constprop.45+0xe1/0xe1 [ 30.557123] [] ? vprintk_emit+0x242/0x850 [ 30.562889] [] ? dump_page_badflags+0x22/0x250 [ 30.569089] [] ? vprintk_emit+0x242/0x850 [ 30.574855] [] df_debug+0x2d/0x30 [ 30.579931] [] do_double_fault+0x10b/0x210 [ 30.585788] [] double_fault+0x2d/0x40 [ 30.591215] [] ? dump_page_badflags+0x180/0x250 [ 30.597509] [] ? dump_page_badflags+0xd/0x250 [ 30.603622] <> [ 30.607097] Dumping ftrace buffer: [ 30.610931] (ftrace buffer empty) [ 30.614612] Kernel Offset: disabled [ 30.618218] Rebooting in 86400 seconds..