[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 22.261681] random: sshd: uninitialized urandom read (32 bytes read, 32 bits of entropy available) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 25.389118] random: sshd: uninitialized urandom read (32 bytes read, 36 bits of entropy available) [ 25.695696] random: sshd: uninitialized urandom read (32 bytes read, 36 bits of entropy available) [ 27.088732] random: sshd: uninitialized urandom read (32 bytes read, 127 bits of entropy available) [ 27.194708] random: nonblocking pool is initialized Warning: Permanently added '10.128.10.35' (ECDSA) to the list of known hosts. [ 32.842507] IPVS: Creating netns size=2552 id=1 net.ipv6.conf.syz_tun.accept_dad = 0 net.ipv6.conf.syz_tun.router_solicitations = 0 executing program [ 32.962987] [ 32.964656] ====================================================== [ 32.970975] [ INFO: possible circular locking dependency detected ] [ 32.977606] 4.4.141-g1b37d68 #71 Not tainted [ 32.981996] ------------------------------------------------------- [ 32.988488] syz-executor587/3838 is trying to acquire lock: [ 32.994188] (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 33.003039] [ 33.003039] but task is already holding lock: [ 33.008991] (&(&q->lock)->rlock){+.-...}, at: [] ipv6_frag_rcv+0x605/0x4fd0 [ 33.018236] [ 33.018236] which lock already depends on the new lock. [ 33.018236] [ 33.026543] [ 33.026543] the existing dependency chain (in reverse order) is: [ 33.034146] -> #1 (&(&q->lock)->rlock){+.-...}: [ 33.039488] [] lock_acquire+0x15e/0x450 [ 33.045746] [] _raw_spin_lock_irqsave+0x4e/0x70 [ 33.052701] [] lock_timer_base+0xd5/0x170 [ 33.059140] [] mod_timer+0x1b7/0xa80 [ 33.065153] [] inet_frag_find+0x71a/0x9c0 [ 33.071580] [] ip_defrag+0x2ed/0x3fe0 [ 33.077657] [] ip_check_defrag+0x3c8/0x7e0 [ 33.084212] [] packet_rcv_fanout+0x52a/0x5e0 [ 33.090943] [] dev_hard_start_xmit+0x644/0x11c0 [ 33.097908] [] sch_direct_xmit+0x2c1/0x6e0 [ 33.104433] [] __dev_queue_xmit+0xef3/0x1c80 [ 33.111123] [] dev_queue_xmit+0x17/0x20 [ 33.117377] [] neigh_resolve_output+0x637/0x790 [ 33.124340] [] ip_finish_output2+0x6ab/0x1110 [ 33.131140] [] ip_do_fragment+0x19cc/0x2190 [ 33.137803] [] ip_fragment.constprop.51+0x143/0x200 [ 33.145158] [] ip_finish_output+0x48a/0xc00 [ 33.151765] [] ip_mc_output+0x233/0x980 [ 33.158025] [] ip_local_out+0x9b/0x180 [ 33.164208] [] ip_send_skb+0x3c/0xc0 [ 33.170230] [] udp_send_skb+0x5c3/0xc60 [ 33.176493] [] udp_sendmsg+0x16c9/0x1c70 [ 33.182873] [] inet_sendmsg+0x203/0x4d0 [ 33.189163] [] sock_sendmsg+0xcc/0x110 [ 33.195370] [] SYSC_sendto+0x21c/0x370 [ 33.201548] [] SyS_sendto+0x40/0x50 [ 33.207458] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 33.214705] -> #0 (_xmit_NETROM){+.-...}: [ 33.219522] [] __lock_acquire+0x3902/0x5270 [ 33.226139] [] lock_acquire+0x15e/0x450 [ 33.232411] [] _raw_spin_lock+0x36/0x50 [ 33.238711] [] sch_direct_xmit+0x23c/0x6e0 [ 33.245235] [] __dev_queue_xmit+0xef3/0x1c80 [ 33.251940] [] dev_queue_xmit+0x17/0x20 [ 33.258226] [] neigh_resolve_output+0x637/0x790 [ 33.265197] [] ip6_finish_output2+0x929/0x1ca0 [ 33.272087] [] ip6_finish_output+0x3b8/0x760 [ 33.278799] [] ip6_output+0x1b8/0x520 [ 33.284881] [] ip6_local_out+0x9b/0x180 [ 33.291143] [] ip6_send_skb+0xa1/0x340 [ 33.297318] [] ip6_push_pending_frames+0xb3/0xe0 [ 33.304350] [] icmpv6_push_pending_frames+0x33c/0x530 [ 33.311816] [] icmp6_send+0x15cd/0x1b80 [ 33.318089] [] icmpv6_param_prob+0x29/0x40 [ 33.324649] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 33.331208] [] ip6_input_finish+0x32e/0x1550 [ 33.337942] [] ip6_input+0xf6/0x200 [ 33.343890] [] ip6_rcv_finish+0x13d/0x640 [ 33.350365] [] ipv6_rcv+0x10cb/0x1cd0 [ 33.356452] [] __netif_receive_skb_core+0x12d6/0x2940 [ 33.363935] [] __netif_receive_skb+0x5b/0x1b0 [ 33.370724] [] process_backlog+0x216/0x6a0 [ 33.377269] [] net_rx_action+0x3a2/0xdb0 [ 33.383607] [] __do_softirq+0x22c/0xa1a [ 33.389860] [] do_softirq_own_stack+0x1c/0x30 [ 33.396633] [] do_softirq.part.16+0x54/0x60 [ 33.403263] [] do_softirq+0x19/0x20 [ 33.409191] [] netif_rx_ni+0xec/0x3a0 [ 33.415313] [] tun_get_user+0xbe7/0x2410 [ 33.421674] [] tun_chr_write_iter+0xd5/0x190 [ 33.428382] [] do_iter_readv_writev+0x13c/0x1e0 [ 33.435343] [] do_readv_writev+0x2e0/0x6e0 [ 33.441887] [] vfs_writev+0x7b/0xb0 [ 33.447804] [] SyS_writev+0xd9/0x250 [ 33.453813] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 33.461049] [ 33.461049] other info that might help us debug this: [ 33.461049] [ 33.469180] Possible unsafe locking scenario: [ 33.469180] [ 33.475222] CPU0 CPU1 [ 33.479881] ---- ---- [ 33.484537] lock(&(&q->lock)->rlock); [ 33.488732] lock(_xmit_NETROM); [ 33.494935] lock(&(&q->lock)->rlock); [ 33.501701] lock(_xmit_NETROM); [ 33.505409] [ 33.505409] *** DEADLOCK *** [ 33.505409] [ 33.511467] 7 locks held by syz-executor587/3838: [ 33.516289] #0: (rcu_read_lock){......}, at: [] process_backlog+0x1b2/0x6a0 [ 33.525760] #1: (rcu_read_lock){......}, at: [] ip6_input_finish+0x0/0x1550 [ 33.535275] #2: (&(&q->lock)->rlock){+.-...}, at: [] ipv6_frag_rcv+0x605/0x4fd0 [ 33.545081] #3: (slock-AF_INET6){+.....}, at: [] icmp6_send+0x7e8/0x1b80 [ 33.554268] #4: (rcu_read_lock){......}, at: [] icmp6_send+0x102b/0x1b80 [ 33.563489] #5: (rcu_read_lock_bh){......}, at: [] ip6_finish_output2+0x1d5/0x1ca0 [ 33.573566] #6: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x1d7/0x1c80 [ 33.583444] [ 33.583444] stack backtrace: [ 33.587939] CPU: 1 PID: 3838 Comm: syz-executor587 Not tainted 4.4.141-g1b37d68 #71 [ 33.595725] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 33.605081] 0000000000000000 b2691544065b0181 ffff8801db306a48 ffffffff81e0e18d [ 33.613103] ffffffff853eb720 ffffffff853ebf90 ffffffff853eb720 ffff8801d8c2d150 [ 33.621147] ffff8801d8c2c800 ffff8801db306a90 ffffffff8140e71b 0000000000000003 [ 33.629201] Call Trace: [ 33.631772] [] dump_stack+0xc1/0x124 [ 33.637887] [] print_circular_bug.cold.50+0x1bd/0x27d [ 33.644720] [] __lock_acquire+0x3902/0x5270 [ 33.650696] [] ? debug_check_no_locks_freed+0x210/0x210 [ 33.657705] [] ? __lock_acquire+0x2c00/0x5270 [ 33.663848] [] ? __dev_get_by_index+0x1a0/0x1a0 [ 33.670175] [] ? __skb_gso_segment+0x490/0x490 [ 33.676430] [] lock_acquire+0x15e/0x450 [ 33.682065] [] ? sch_direct_xmit+0x23c/0x6e0 [ 33.688129] [] _raw_spin_lock+0x36/0x50 [ 33.693761] [] ? sch_direct_xmit+0x23c/0x6e0 [ 33.699811] [] sch_direct_xmit+0x23c/0x6e0 [ 33.705695] [] ? dev_watchdog+0x7f0/0x7f0 [ 33.711482] [] __dev_queue_xmit+0xef3/0x1c80 [ 33.717540] [] ? __dev_queue_xmit+0x1d7/0x1c80 [ 33.723781] [] ? debug_check_no_locks_freed+0x210/0x210 [ 33.730799] [] ? ip6t_do_table+0xac3/0x17e0 [ 33.736791] [] ? netdev_pick_tx+0x2c0/0x2c0 [ 33.742777] [] ? mark_held_locks+0xc7/0x130 [ 33.748755] [] ? memcpy+0x45/0x50 [ 33.753864] [] dev_queue_xmit+0x17/0x20 [ 33.759511] [] neigh_resolve_output+0x637/0x790 [ 33.765825] [] ? ip6_finish_output2+0x929/0x1ca0 [ 33.772214] [] ip6_finish_output2+0x929/0x1ca0 [ 33.778532] [] ? ip6_finish_output2+0x1d5/0x1ca0 [ 33.784947] [] ? ip6_sk_dst_lookup_flow+0x580/0x580 [ 33.791618] [] ? ip6_mtu+0x217/0x340 [ 33.796979] [] ip6_finish_output+0x3b8/0x760 [ 33.803025] [] ip6_output+0x1b8/0x520 [ 33.808472] [] ? ip6_finish_output+0x760/0x760 [ 33.814706] [] ? ip6_fragment+0x3510/0x3510 [ 33.820690] [] ? ip6_setup_cork+0x11a0/0x11a0 [ 33.826835] [] ip6_local_out+0x9b/0x180 [ 33.832457] [] ip6_send_skb+0xa1/0x340 [ 33.837992] [] ip6_push_pending_frames+0xb3/0xe0 [ 33.844388] [] icmpv6_push_pending_frames+0x33c/0x530 [ 33.851236] [] icmp6_send+0x15cd/0x1b80 [ 33.856869] [] ? icmpv6_push_pending_frames+0x530/0x530 [ 33.863902] [] ? trace_hardirqs_on_caller+0x266/0x590 [ 33.870982] [] ? mod_timer+0x434/0xa80 [ 33.876707] [] ? ipv6_frag_rcv+0x605/0x4fd0 [ 33.882679] [] icmpv6_param_prob+0x29/0x40 [ 33.888557] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 33.894445] [] ? ip6_frag_expire+0x60/0x60 [ 33.900335] [] ? raw6_local_deliver+0x3d5/0x7d0 [ 33.906685] [] ip6_input_finish+0x32e/0x1550 [ 33.912726] [] ? ip6_rcv_finish+0x640/0x640 [ 33.918700] [] ip6_input+0xf6/0x200 [ 33.923959] [] ? ipv6_rcv+0x1cd0/0x1cd0 [ 33.929595] [] ? ip6_rcv_finish+0x640/0x640 [ 33.935591] [] ip6_rcv_finish+0x13d/0x640 [ 33.941393] [] ? sk_receive_skb+0x940/0x940 [ 33.947360] [] ipv6_rcv+0x10cb/0x1cd0 [ 33.952806] [] ? ipv6_rcv+0xf8/0x1cd0 [ 33.958242] [] ? ip6_input_finish+0x1550/0x1550 [ 33.964541] [] ? ip6_make_skb+0x400/0x400 [ 33.970317] [] ? packet_rcv_fanout+0x170/0x5e0 [ 33.976539] [] ? ip6_input_finish+0x1550/0x1550 [ 33.982891] [] __netif_receive_skb_core+0x12d6/0x2940 [ 33.989738] [] ? dev_cpu_callback+0x660/0x660 [ 33.995877] [] ? kmem_cache_free+0xbe/0x340 [ 34.001862] [] ? rcu_process_callbacks+0x927/0x1440 [ 34.008529] [] ? __do_softirq+0x22c/0xa1a [ 34.014350] [] ? do_softirq_own_stack+0x1c/0x30 [ 34.020698] [] ? do_softirq.part.16+0x54/0x60 [ 34.026860] [] ? __local_bh_enable_ip+0xc6/0xd0 [ 34.033192] [] ? lock_sock_nested+0xdc/0x120 [ 34.039249] [] ? tcp_sendmsg+0xaf/0x2b00 [ 34.044966] [] ? inet_sendmsg+0x203/0x4d0 [ 34.050746] [] ? sock_sendmsg+0xcc/0x110 [ 34.056446] [] __netif_receive_skb+0x5b/0x1b0 [ 34.062592] [] process_backlog+0x216/0x6a0 [ 34.068493] [] ? process_backlog+0x1b2/0x6a0 [ 34.074558] [] net_rx_action+0x3a2/0xdb0 [ 34.080273] [] ? napi_complete_done+0x1f0/0x1f0 [ 34.086598] [] ? check_preemption_disabled+0x3b/0x170 [ 34.093433] [] __do_softirq+0x22c/0xa1a [ 34.099059] [] do_softirq_own_stack+0x1c/0x30 [ 34.105194] [] do_softirq.part.16+0x54/0x60 [ 34.111887] [] do_softirq+0x19/0x20 [ 34.117145] [] netif_rx_ni+0xec/0x3a0 [ 34.122577] [] tun_get_user+0xbe7/0x2410 [ 34.128291] [] ? tun_net_xmit+0xe60/0xe60 [ 34.134076] [] ? __tun_get+0x126/0x230 [ 34.139621] [] tun_chr_write_iter+0xd5/0x190 [ 34.145715] [] do_iter_readv_writev+0x13c/0x1e0 [ 34.152033] [] ? tun_sendmsg+0x140/0x140 [ 34.157744] [] ? vfs_iter_read+0x270/0x270 [ 34.163610] [] ? rw_verify_area+0x100/0x300 [ 34.169569] [] ? tun_sendmsg+0x140/0x140 [ 34.175265] [] do_readv_writev+0x2e0/0x6e0 [ 34.181139] [] ? vfs_write+0x4e0/0x4e0 [ 34.186668] [] ? _raw_spin_unlock+0x2c/0x50 [ 34.192636] [] ? do_huge_pmd_anonymous_page+0x38c/0x9d0 [ 34.199643] [] ? handle_mm_fault+0xbf7/0x30b0 [ 34.205773] [] ? SYSC_connect+0x22a/0x300 [ 34.211573] [] vfs_writev+0x7b/0xb0 [ 34.216836] [] SyS_writev+0xd9/0x250 [ 34.222184] [] ? SyS_readv+0x250/0x250 [ 34.227705] [] ? lockdep_sys_exit_thunk+0x12/0x14 [ 34.234196] [] entry_SYSCALL_64_fastpath+0x22/0x9e