[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 22.158218] random: sshd: uninitialized urandom read (32 bytes read, 36 bits of entropy available) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [ 22.986486] random: sshd: uninitialized urandom read (32 bytes read, 37 bits of entropy available) Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 23.468518] random: sshd: uninitialized urandom read (32 bytes read, 39 bits of entropy available) [ 24.432472] random: nonblocking pool is initialized Warning: Permanently added '10.128.0.27' (ECDSA) to the list of known hosts. net.ipv6.conf.syz_tun.accept_dad = 0 [ 31.128703] IPVS: Creating netns size=2552 id=1 net.ipv6.conf.syz_tun.router_solicitations = 0 executing program [ 31.226528] [ 31.228181] ====================================================== [ 31.234469] [ INFO: possible circular locking dependency detected ] [ 31.240860] 4.4.138-g07c0138 #62 Not tainted [ 31.245235] ------------------------------------------------------- [ 31.251619] syz-executor011/3847 is trying to acquire lock: [ 31.257310] (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 31.266109] [ 31.266109] but task is already holding lock: [ 31.272058] (&(&q->lock)->rlock){+.-...}, at: [] ipv6_frag_rcv+0x605/0x4fd0 [ 31.281290] [ 31.281290] which lock already depends on the new lock. [ 31.281290] [ 31.289581] [ 31.289581] the existing dependency chain (in reverse order) is: [ 31.297183] -> #1 (&(&q->lock)->rlock){+.-...}: [ 31.303334] [] lock_acquire+0x15e/0x450 [ 31.309625] [] _raw_spin_lock_irqsave+0x4e/0x70 [ 31.316563] [] lock_timer_base+0xd5/0x170 [ 31.322991] [] mod_timer+0x1b7/0xa80 [ 31.328984] [] inet_frag_find+0x71a/0x9c0 [ 31.335425] [] ip_defrag+0x2ed/0x3fe0 [ 31.341497] [] ip_check_defrag+0x3c8/0x7e0 [ 31.348007] [] packet_rcv_fanout+0x52a/0x5e0 [ 31.354683] [] dev_hard_start_xmit+0x644/0x11c0 [ 31.361625] [] sch_direct_xmit+0x2c1/0x6e0 [ 31.368157] [] __dev_queue_xmit+0xef3/0x1c80 [ 31.374846] [] dev_queue_xmit+0x17/0x20 [ 31.381095] [] neigh_resolve_output+0x637/0x790 [ 31.388043] [] ip_finish_output2+0x6ab/0x1110 [ 31.394807] [] ip_do_fragment+0x19cc/0x2190 [ 31.401394] [] ip_fragment.constprop.51+0x143/0x200 [ 31.408684] [] ip_finish_output+0x48a/0xc00 [ 31.415271] [] ip_mc_output+0x233/0x980 [ 31.421778] [] ip_local_out+0x9b/0x180 [ 31.427930] [] ip_send_skb+0x3c/0xc0 [ 31.433919] [] udp_send_skb+0x5c3/0xc60 [ 31.440163] [] udp_sendmsg+0x16c9/0x1c70 [ 31.446500] [] inet_sendmsg+0x203/0x4d0 [ 31.452766] [] sock_sendmsg+0xcc/0x110 [ 31.458934] [] SYSC_sendto+0x21c/0x370 [ 31.465092] [] SyS_sendto+0x40/0x50 [ 31.470996] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 31.478201] -> #0 (_xmit_NETROM){+.-...}: [ 31.483011] [] __lock_acquire+0x3902/0x5270 [ 31.489610] [] lock_acquire+0x15e/0x450 [ 31.495865] [] _raw_spin_lock+0x36/0x50 [ 31.502191] [] sch_direct_xmit+0x23c/0x6e0 [ 31.508784] [] __dev_queue_xmit+0xef3/0x1c80 [ 31.515458] [] dev_queue_xmit+0x17/0x20 [ 31.521701] [] neigh_resolve_output+0x637/0x790 [ 31.528629] [] ip6_finish_output2+0x929/0x1ca0 [ 31.535474] [] ip6_finish_output+0x3b8/0x760 [ 31.542142] [] ip6_output+0x1b8/0x520 [ 31.548204] [] NF_HOOK_THRESH.constprop.29+0x11f/0x310 [ 31.555749] [] ndisc_send_skb+0x7e7/0xf20 [ 31.562168] [] ndisc_send_ns+0x501/0x700 [ 31.568494] [] ndisc_solicit+0x2a2/0x430 [ 31.574820] [] neigh_probe+0xca/0x100 [ 31.580887] [] __neigh_event_send+0x2a0/0xc50 [ 31.587641] [] neigh_resolve_output+0x4eb/0x790 [ 31.594580] [] ip6_finish_output2+0x929/0x1ca0 [ 31.601428] [] ip6_finish_output+0x3b8/0x760 [ 31.608102] [] ip6_output+0x1b8/0x520 [ 31.614172] [] ip6_local_out+0x9b/0x180 [ 31.620428] [] ip6_send_skb+0xa1/0x340 [ 31.626589] [] ip6_push_pending_frames+0xb3/0xe0 [ 31.633618] [] icmpv6_push_pending_frames+0x33c/0x530 [ 31.641080] [] icmp6_send+0x15cd/0x1b80 [ 31.647330] [] icmpv6_param_prob+0x29/0x40 [ 31.653850] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 31.660358] [] ip6_input_finish+0x32e/0x1550 [ 31.667040] [] ip6_input+0xf6/0x200 [ 31.672928] [] ip6_rcv_finish+0x13d/0x640 [ 31.679339] [] ipv6_rcv+0x10cb/0x1cd0 [ 31.685416] [] __netif_receive_skb_core+0x12d6/0x2940 [ 31.692898] [] __netif_receive_skb+0x5b/0x1b0 [ 31.699683] [] process_backlog+0x216/0x6a0 [ 31.706190] [] net_rx_action+0x3a2/0xdb0 [ 31.712524] [] __do_softirq+0x22c/0xa1a [ 31.718782] [] do_softirq_own_stack+0x1c/0x30 [ 31.725552] [] do_softirq.part.16+0x54/0x60 [ 31.732149] [] do_softirq+0x19/0x20 [ 31.738045] [] netif_rx_ni+0xec/0x3a0 [ 31.744125] [] tun_get_user+0xbe7/0x2410 [ 31.750478] [] tun_chr_write_iter+0xd5/0x190 [ 31.757159] [] do_iter_readv_writev+0x13c/0x1e0 [ 31.764101] [] do_readv_writev+0x2e0/0x6e0 [ 31.770613] [] vfs_writev+0x7b/0xb0 [ 31.776512] [] SyS_writev+0xd9/0x250 [ 31.782502] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 31.789708] [ 31.789708] other info that might help us debug this: [ 31.789708] [ 31.797823] Possible unsafe locking scenario: [ 31.797823] [ 31.803852] CPU0 CPU1 [ 31.808497] ---- ---- [ 31.813140] lock(&(&q->lock)->rlock); [ 31.817350] lock(_xmit_NETROM); [ 31.823550] lock(&(&q->lock)->rlock); [ 31.830307] lock(_xmit_NETROM); [ 31.833982] [ 31.833982] *** DEADLOCK *** [ 31.833982] [ 31.840029] 9 locks held by syz-executor011/3847: [ 31.844867] #0: (rcu_read_lock){......}, at: [] process_backlog+0x1b2/0x6a0 [ 31.854860] #1: (rcu_read_lock){......}, at: [] ip6_input_finish+0x0/0x1550 [ 31.864313] #2: (&(&q->lock)->rlock){+.-...}, at: [] ipv6_frag_rcv+0x605/0x4fd0 [ 31.874103] #3: (slock-AF_INET6){+.....}, at: [] icmp6_send+0x7e8/0x1b80 [ 31.883273] #4: (rcu_read_lock){......}, at: [] icmp6_send+0x102b/0x1b80 [ 31.892432] #5: (rcu_read_lock_bh){......}, at: [] ip6_finish_output2+0x1d5/0x1ca0 [ 31.902452] #6: (rcu_read_lock){......}, at: [] ndisc_send_skb+0x637/0xf20 [ 31.911794] #7: (rcu_read_lock_bh){......}, at: [] ip6_finish_output2+0x1d5/0x1ca0 [ 31.921830] #8: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x1d7/0x1c80 [ 31.931734] [ 31.931734] stack backtrace: [ 31.936215] CPU: 0 PID: 3847 Comm: syz-executor011 Not tainted 4.4.138-g07c0138 #62 [ 31.943990] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 31.953318] 0000000000000000 2ae3f3d68d4df4d2 ffff8801db2062d8 ffffffff81e0ed0d [ 31.961321] ffffffff853eba40 ffffffff853ec2b0 ffffffff853eba40 ffff8801d8c15150 [ 31.969337] ffff8801d8c14800 ffff8801db206320 ffffffff8140e6ab 0000000000000003 [ 31.977333] Call Trace: [ 31.979897] [] dump_stack+0xc1/0x124 [ 31.985979] [] print_circular_bug.cold.50+0x1bd/0x27d [ 31.992802] [] __lock_acquire+0x3902/0x5270 [ 31.998757] [] ? debug_check_no_locks_freed+0x210/0x210 [ 32.005751] [] ? __lock_acquire+0x2c00/0x5270 [ 32.011880] [] ? __dev_get_by_index+0x1a0/0x1a0 [ 32.018174] [] ? __skb_gso_segment+0x490/0x490 [ 32.024381] [] lock_acquire+0x15e/0x450 [ 32.029978] [] ? sch_direct_xmit+0x23c/0x6e0 [ 32.036019] [] _raw_spin_lock+0x36/0x50 [ 32.041632] [] ? sch_direct_xmit+0x23c/0x6e0 [ 32.047670] [] sch_direct_xmit+0x23c/0x6e0 [ 32.053531] [] ? dev_watchdog+0x7f0/0x7f0 [ 32.059308] [] __dev_queue_xmit+0xef3/0x1c80 [ 32.065344] [] ? __dev_queue_xmit+0x1d7/0x1c80 [ 32.071558] [] ? debug_check_no_locks_freed+0x210/0x210 [ 32.078565] [] ? netdev_pick_tx+0x2c0/0x2c0 [ 32.084514] [] ? mark_held_locks+0xc7/0x130 [ 32.090485] [] ? memcpy+0x45/0x50 [ 32.095568] [] dev_queue_xmit+0x17/0x20 [ 32.101166] [] neigh_resolve_output+0x637/0x790 [ 32.107465] [] ? ip6_finish_output2+0x929/0x1ca0 [ 32.113859] [] ip6_finish_output2+0x929/0x1ca0 [ 32.120074] [] ? ip6_finish_output2+0x1d5/0x1ca0 [ 32.126463] [] ? ip6_sk_dst_lookup_flow+0x580/0x580 [ 32.133103] [] ? ip6_mtu+0x217/0x340 [ 32.138445] [] ip6_finish_output+0x3b8/0x760 [ 32.144497] [] ip6_output+0x1b8/0x520 [ 32.149948] [] ? ip6_finish_output+0x760/0x760 [ 32.156168] [] ? nf_iterate+0x210/0x210 [ 32.161772] [] ? ip6_fragment+0x3510/0x3510 [ 32.167729] [] NF_HOOK_THRESH.constprop.29+0x11f/0x310 [ 32.174627] [] ? ndisc_error_report+0x1a0/0x1a0 [ 32.180918] [] ? ndisc_parse_options.part.28+0x390/0x390 [ 32.187998] [] ndisc_send_skb+0x7e7/0xf20 [ 32.193773] [] ? ndisc_send_skb+0x637/0xf20 [ 32.199717] [] ? pndisc_destructor+0x200/0x200 [ 32.205924] [] ? ip6_input+0xf6/0x200 [ 32.211354] [] ? ndisc_fill_addr_option+0x19a/0x1f0 [ 32.217993] [] ndisc_send_ns+0x501/0x700 [ 32.223676] [] ? trace_hardirqs_on+0xd/0x10 [ 32.229624] [] ? ndisc_netdev_event+0x390/0x390 [ 32.235914] [] ? ipv6_chk_addr_and_flags+0x3a4/0x530 [ 32.242641] [] ? ipv6_chk_addr_and_flags+0x69/0x530 [ 32.249299] [] ndisc_solicit+0x2a2/0x430 [ 32.254993] [] ? ndisc_send_ns+0x700/0x700 [ 32.260856] [] ? neigh_probe+0x6f/0x100 [ 32.266469] [] ? ndisc_send_ns+0x700/0x700 [ 32.272329] [] neigh_probe+0xca/0x100 [ 32.277752] [] __neigh_event_send+0x2a0/0xc50 [ 32.283880] [] ? __local_bh_enable_ip+0x6a/0xd0 [ 32.290175] [] neigh_resolve_output+0x4eb/0x790 [ 32.296469] [] ip6_finish_output2+0x929/0x1ca0 [ 32.302700] [] ? ip6_finish_output2+0x1d5/0x1ca0 [ 32.309110] [] ? ip6_sk_dst_lookup_flow+0x580/0x580 [ 32.315754] [] ? ip6_mtu+0x217/0x340 [ 32.321122] [] ip6_finish_output+0x3b8/0x760 [ 32.327185] [] ip6_output+0x1b8/0x520 [ 32.332612] [] ? ip6_finish_output+0x760/0x760 [ 32.338827] [] ? ip6_fragment+0x3510/0x3510 [ 32.344781] [] ? ip6_setup_cork+0x11a0/0x11a0 [ 32.350904] [] ip6_local_out+0x9b/0x180 [ 32.356518] [] ip6_send_skb+0xa1/0x340 [ 32.362057] [] ip6_push_pending_frames+0xb3/0xe0 [ 32.368473] [] icmpv6_push_pending_frames+0x33c/0x530 [ 32.368485] [] icmp6_send+0x15cd/0x1b80 [ 32.368491] [] ? icmpv6_push_pending_frames+0x530/0x530 [ 32.368500] [] ? trace_hardirqs_on_caller+0x266/0x590 [ 32.368508] [] ? mod_timer+0x434/0xa80 [ 32.368516] [] ? ipv6_frag_rcv+0x605/0x4fd0 [ 32.368531] [] icmpv6_param_prob+0x29/0x40 [ 32.368538] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 32.368545] [] ? ip6_frag_expire+0x60/0x60 [ 32.368551] [] ? raw6_local_deliver+0x3d5/0x7d0 [ 32.368561] [] ip6_input_finish+0x32e/0x1550 [ 32.368568] [] ? ip6_rcv_finish+0x640/0x640 [ 32.368575] [] ip6_input+0xf6/0x200 [ 32.368581] [] ? ipv6_rcv+0x1cd0/0x1cd0 [ 32.368587] [] ? ip6_rcv_finish+0x640/0x640 [ 32.368594] [] ip6_rcv_finish+0x13d/0x640 [ 32.368601] [] ? sk_receive_skb+0x940/0x940 [ 32.368607] [] ipv6_rcv+0x10cb/0x1cd0 [ 32.368613] [] ? ipv6_rcv+0xf8/0x1cd0 [ 32.368620] [] ? ip6_input_finish+0x1550/0x1550 [ 32.368627] [] ? ip6_make_skb+0x400/0x400 [ 32.368633] [] ? packet_rcv_fanout+0x170/0x5e0 [ 32.368640] [] ? ip6_input_finish+0x1550/0x1550 [ 32.368647] [] __netif_receive_skb_core+0x12d6/0x2940 [ 32.368654] [] ? dev_cpu_callback+