[....] 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[ 19.496752] random: sshd: uninitialized urandom read (32 bytes read, 32 bits of entropy available) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [ 20.646907] random: sshd: uninitialized urandom read (32 bytes read, 34 bits of entropy available) Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 20.977940] random: sshd: uninitialized urandom read (32 bytes read, 34 bits of entropy available) [ 21.983022] random: nonblocking pool is initialized Warning: Permanently added '10.128.0.56' (ECDSA) to the list of known hosts. net.ipv6.conf.syz_tun.accept_dad = 0 net.ipv6.conf.syz_tun.router_solicitations = 0 [ 29.822391] IPVS: Creating netns size=2552 id=1 executing program [ 29.913622] [ 29.915259] ====================================================== [ 29.921545] [ INFO: possible circular locking dependency detected ] [ 29.927917] 4.4.137-ga2e2217 #61 Not tainted [ 29.932291] ------------------------------------------------------- [ 29.938664] syz-executor191/3781 is trying to acquire lock: [ 29.944340] (&(&q->lock)->rlock){+.-...}, at: [] ip_defrag+0x318/0x3fe0 [ 29.953189] [ 29.953189] but task is already holding lock: [ 29.959128] (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 29.967904] [ 29.967904] which lock already depends on the new lock. [ 29.967904] [ 29.976189] [ 29.976189] the existing dependency chain (in reverse order) is: [ 29.983780] -> #1 (_xmit_NETROM){+.-...}: [ 29.988536] [] lock_acquire+0x15e/0x450 [ 29.994773] [] _raw_spin_lock_irqsave+0x4e/0x70 [ 30.001708] [] depot_save_stack+0x211/0x610 [ 30.008289] [] save_stack+0xa9/0xd0 [ 30.014174] [] kasan_kmalloc+0xc7/0xe0 [ 30.020320] [] kasan_slab_alloc+0x12/0x20 [ 30.026725] [] kmem_cache_alloc+0xbe/0x2a0 [ 30.033217] [] inet_getpeer.part.5+0xeac/0x15a0 [ 30.040150] [] inet_getpeer+0x55b/0x6f0 [ 30.046385] [] icmp6_send+0x17c5/0x1b80 [ 30.052617] [] icmpv6_param_prob+0x29/0x40 [ 30.059106] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 30.065598] [] ip6_input_finish+0x32e/0x1550 [ 30.072262] [] ip6_input+0xf6/0x200 [ 30.078145] [] ip6_rcv_finish+0x13d/0x640 [ 30.084545] [] ipv6_rcv+0x10cb/0x1cd0 [ 30.090603] [] __netif_receive_skb_core+0x12d6/0x2940 [ 30.098052] [] __netif_receive_skb+0x5b/0x1b0 [ 30.104806] [] process_backlog+0x216/0x6a0 [ 30.111296] [] net_rx_action+0x3a2/0xdb0 [ 30.117613] [] __do_softirq+0x22c/0xa1a [ 30.123844] [] do_softirq_own_stack+0x1c/0x30 [ 30.130599] [] do_softirq.part.16+0x54/0x60 [ 30.137180] [] do_softirq+0x19/0x20 [ 30.143063] [] netif_rx_ni+0xec/0x3a0 [ 30.149129] [] tun_get_user+0xbe7/0x2410 [ 30.155456] [] tun_chr_write_iter+0xd5/0x190 [ 30.162120] [] do_iter_readv_writev+0x13c/0x1e0 [ 30.169045] [] do_readv_writev+0x2e0/0x6e0 [ 30.175536] [] vfs_writev+0x7b/0xb0 [ 30.181417] [] SyS_writev+0xd9/0x250 [ 30.187387] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 30.194580] -> #0 (&(&q->lock)->rlock){+.-...}: [ 30.199861] [] __lock_acquire+0x3902/0x5270 [ 30.206441] [] lock_acquire+0x15e/0x450 [ 30.212671] [] _raw_spin_lock+0x36/0x50 [ 30.218899] [] ip_defrag+0x318/0x3fe0 [ 30.224971] [] ip_check_defrag+0x3c8/0x7e0 [ 30.231463] [] packet_rcv_fanout+0x52a/0x5e0 [ 30.238130] [] dev_hard_start_xmit+0x644/0x11c0 [ 30.245058] [] sch_direct_xmit+0x2c1/0x6e0 [ 30.251550] [] __dev_queue_xmit+0xef3/0x1c80 [ 30.258213] [] dev_queue_xmit+0x17/0x20 [ 30.264445] [] neigh_resolve_output+0x637/0x790 [ 30.271371] [] ip_finish_output2+0x6ab/0x1110 [ 30.278120] [] ip_do_fragment+0x19cc/0x2190 [ 30.284700] [] ip_fragment.constprop.51+0x143/0x200 [ 30.291973] [] ip_finish_output+0x48a/0xc00 [ 30.298553] [] ip_mc_output+0x233/0x980 [ 30.304786] [] ip_local_out+0x9b/0x180 [ 30.310941] [] ip_send_skb+0x3c/0xc0 [ 30.316913] [] udp_send_skb+0x5c3/0xc60 [ 30.323144] [] udp_sendmsg+0x16c9/0x1c70 [ 30.329463] [] inet_sendmsg+0x203/0x4d0 [ 30.335702] [] sock_sendmsg+0xcc/0x110 [ 30.341853] [] SYSC_sendto+0x21c/0x370 [ 30.347998] [] SyS_sendto+0x40/0x50 [ 30.353880] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 30.361071] [ 30.361071] other info that might help us debug this: [ 30.361071] [ 30.369181] Possible unsafe locking scenario: [ 30.369181] [ 30.375206] CPU0 CPU1 [ 30.379841] ---- ---- [ 30.384476] lock(_xmit_NETROM); [ 30.388130] lock(&(&q->lock)->rlock); [ 30.394823] lock(_xmit_NETROM); [ 30.400997] lock(&(&q->lock)->rlock); [ 30.405173] [ 30.405173] *** DEADLOCK *** [ 30.405173] [ 30.411207] 4 locks held by syz-executor191/3781: [ 30.416016] #0: (rcu_read_lock_bh){......}, at: [] ip_finish_output2+0x212/0x1110 [ 30.425941] #1: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x1d7/0x1c80 [ 30.435770] #2: (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 30.445080] #3: (rcu_read_lock){......}, at: [] dev_hard_start_xmit+0xa8/0x11c0 [ 30.454819] [ 30.454819] stack backtrace: [ 30.459286] CPU: 0 PID: 3781 Comm: syz-executor191 Not tainted 4.4.137-ga2e2217 #61 [ 30.467047] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 30.476373] 0000000000000000 9273ddb5888d2d46 ffff8801d966ed38 ffffffff81e0ee0d [ 30.484345] ffffffff853eb3c0 ffffffff853eba80 ffffffff853eb3c0 ffff8800aea03950 [ 30.492318] ffff8800aea03000 ffff8801d966ed80 ffffffff8140e6ab 0000000000000003 [ 30.500293] Call Trace: [ 30.502849] [] dump_stack+0xc1/0x124 [ 30.508184] [] print_circular_bug.cold.50+0x1bd/0x27d [ 30.514994] [] __lock_acquire+0x3902/0x5270 [ 30.520937] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.527917] [] ? trace_hardirqs_on_caller+0x266/0x590 [ 30.534727] [] lock_acquire+0x15e/0x450 [ 30.540321] [] ? ip_defrag+0x318/0x3fe0 [ 30.545913] [] ? inet_frag_find+0x22e/0x9c0 [ 30.551862] [] _raw_spin_lock+0x36/0x50 [ 30.557455] [] ? ip_defrag+0x318/0x3fe0 [ 30.563048] [] ip_defrag+0x318/0x3fe0 [ 30.568469] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.575452] [] ? memcpy+0x45/0x50 [ 30.580523] [] ? ip_expire+0x770/0x770 [ 30.586036] [] ip_check_defrag+0x3c8/0x7e0 [ 30.591895] [] ? ip_defrag+0x3fe0/0x3fe0 [ 30.597576] [] packet_rcv_fanout+0x52a/0x5e0 [ 30.603603] [] ? packet_bind+0x190/0x190 [ 30.609284] [] dev_hard_start_xmit+0x644/0x11c0 [ 30.615574] [] ? dev_hard_start_xmit+0xa8/0x11c0 [ 30.621950] [] sch_direct_xmit+0x2c1/0x6e0 [ 30.627801] [] ? dev_watchdog+0x7f0/0x7f0 [ 30.633568] [] __dev_queue_xmit+0xef3/0x1c80 [ 30.639596] [] ? __dev_queue_xmit+0x1d7/0x1c80 [ 30.645807] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.652795] [] ? netdev_pick_tx+0x2c0/0x2c0 [ 30.658738] [] ? memcpy+0x45/0x50 [ 30.663820] [] dev_queue_xmit+0x17/0x20 [ 30.669413] [] neigh_resolve_output+0x637/0x790 [ 30.675703] [] ? ip_finish_output2+0x6ab/0x1110 [ 30.681988] [] ip_finish_output2+0x6ab/0x1110 [ 30.688102] [] ? ip_finish_output2+0x212/0x1110 [ 30.694391] [] ? nf_ct_deliver_cached_events+0x335/0x560 [ 30.701458] [] ? ip_copy_metadata+0x700/0x700 [ 30.707573] [] ip_do_fragment+0x19cc/0x2190 [ 30.713513] [] ? ip_copy_metadata+0x700/0x700 [ 30.719627] [] ip_fragment.constprop.51+0x143/0x200 [ 30.726269] [] ip_finish_output+0x48a/0xc00 [ 30.732211] [] ip_mc_output+0x233/0x980 [ 30.737803] [] ? ip_queue_xmit+0x1af0/0x1af0 [ 30.743827] [] ? ip_make_skb+0x116/0x210 [ 30.749507] [] ? ip_fragment.constprop.51+0x200/0x200 [ 30.756316] [] ? ip_flush_pending_frames+0x30/0x30 [ 30.762861] [] ip_local_out+0x9b/0x180 [ 30.768367] [] ip_send_skb+0x3c/0xc0 [ 30.773700] [] udp_send_skb+0x5c3/0xc60 [ 30.779294] [] udp_sendmsg+0x16c9/0x1c70 [ 30.784976] [] ? ip_reply_glue_bits+0xc0/0xc0 [ 30.791090] [] ? udp4_lib_lookup+0x60/0x60 [ 30.796945] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.803930] [] ? sock_has_perm+0x1c1/0x400 [ 30.809791] [] ? sock_has_perm+0x29f/0x400 [ 30.815646] [] ? sock_has_perm+0x9f/0x400 [ 30.821414] [] ? inet_sendmsg+0x143/0x4d0 [ 30.827179] [] inet_sendmsg+0x203/0x4d0 [ 30.832769] [] ? inet_sendmsg+0x73/0x4d0 [ 30.838449] [] ? inet_recvmsg+0x4c0/0x4c0 [ 30.844218] [] sock_sendmsg+0xcc/0x110 [ 30.849727] [] SYSC_sendto+0x21c/0x370 [ 30.855234] [] ? SYSC_connect+0x300/0x300 [ 30.861003] [] ? _raw_spin_unlock+0x2c/0x50 [ 30.866945] [] ? do_huge_pmd_anonymous_page+0x38c/0x9d0 [ 30.873928] [] ? handle_mm_fault+0xbf7/0x30b0 [ 30.880043] [] ? SYSC_connect+0x22a/0x300 [ 30.885811] [] ? __do_page_fault+0x385/0xa10 [ 30.891836] [] ? retint_user+0x18/0x3c [ 30.897344] [] SyS_sendto+0x40/0x50 [ 30.902590] [] entry_SYSCALL_64_fastpath+0x22/0x9e