[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 19.708629] random: sshd: uninitialized urandom read (32 bytes read, 31 bits of entropy available) [?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 22.076762] random: sshd: uninitialized urandom read (32 bytes read, 35 bits of entropy available) [ 22.304731] random: sshd: uninitialized urandom read (32 bytes read, 35 bits of entropy available) [ 23.633261] random: sshd: uninitialized urandom read (32 bytes read, 117 bits of entropy available) [ 25.064663] random: sshd: uninitialized urandom read (32 bytes read, 122 bits of entropy available) Warning: Permanently added '10.128.0.12' (ECDSA) to the list of known hosts. [ 30.593405] random: sshd: uninitialized urandom read (32 bytes read, 125 bits of entropy available) net.ipv6.conf.syz_tun.accept_dad = 0 [ 30.695723] IPVS: Creating netns size=2552 id=1 net.ipv6.conf.syz_tun.router_solicitations = 0 executing program [ 30.795597] [ 30.797256] ====================================================== [ 30.804005] [ INFO: possible circular locking dependency detected ] [ 30.810383] 4.4.140-ged9bdc8 #68 Not tainted [ 30.814781] ------------------------------------------------------- [ 30.821183] syz-executor219/3720 is trying to acquire lock: [ 30.826862] (&(&q->lock)->rlock){+.-...}, at: [] ip_defrag+0x318/0x3fe0 [ 30.835991] [ 30.835991] but task is already holding lock: [ 30.842263] (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 30.851053] [ 30.851053] which lock already depends on the new lock. [ 30.851053] [ 30.859365] [ 30.859365] the existing dependency chain (in reverse order) is: [ 30.866974] -> #1 (_xmit_NETROM){+.-...}: [ 30.871747] [] lock_acquire+0x15e/0x450 [ 30.878015] [] _raw_spin_lock_irqsave+0x4e/0x70 [ 30.884950] [] depot_save_stack+0x211/0x610 [ 30.891568] [] save_stack+0xa9/0xd0 [ 30.897454] [] kasan_kmalloc+0xc7/0xe0 [ 30.903602] [] kasan_slab_alloc+0x12/0x20 [ 30.910024] [] kmem_cache_alloc+0xbe/0x2a0 [ 30.916533] [] inet_getpeer.part.5+0xeac/0x15a0 [ 30.923475] [] inet_getpeer+0x55b/0x6f0 [ 30.929749] [] icmp6_send+0x17c5/0x1b80 [ 30.936001] [] icmpv6_param_prob+0x29/0x40 [ 30.942505] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 30.949026] [] ip6_input_finish+0x32e/0x1550 [ 30.955715] [] ip6_input+0xf6/0x200 [ 30.961601] [] ip6_rcv_finish+0x13d/0x640 [ 30.968027] [] ipv6_rcv+0x10cb/0x1cd0 [ 30.974106] [] __netif_receive_skb_core+0x12d6/0x2940 [ 30.981561] [] __netif_receive_skb+0x5b/0x1b0 [ 30.988328] [] process_backlog+0x216/0x6a0 [ 30.994824] [] net_rx_action+0x3a2/0xdb0 [ 31.001152] [] __do_softirq+0x22c/0xa1a [ 31.007391] [] do_softirq_own_stack+0x1c/0x30 [ 31.014179] [] do_softirq.part.16+0x54/0x60 [ 31.020888] [] do_softirq+0x19/0x20 [ 31.026811] [] netif_rx_ni+0xec/0x3a0 [ 31.032877] [] tun_get_user+0xbe7/0x2410 [ 31.039205] [] tun_chr_write_iter+0xd5/0x190 [ 31.045880] [] do_iter_readv_writev+0x13c/0x1e0 [ 31.052816] [] do_readv_writev+0x2e0/0x6e0 [ 31.059313] [] vfs_writev+0x7b/0xb0 [ 31.065199] [] SyS_writev+0xd9/0x250 [ 31.071172] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 31.078365] -> #0 (&(&q->lock)->rlock){+.-...}: [ 31.083659] [] __lock_acquire+0x3902/0x5270 [ 31.090258] [] lock_acquire+0x15e/0x450 [ 31.096498] [] _raw_spin_lock+0x36/0x50 [ 31.102736] [] ip_defrag+0x318/0x3fe0 [ 31.108803] [] ip_check_defrag+0x3c8/0x7e0 [ 31.115305] [] packet_rcv_fanout+0x52a/0x5e0 [ 31.121996] [] dev_hard_start_xmit+0x644/0x11c0 [ 31.128928] [] sch_direct_xmit+0x2c1/0x6e0 [ 31.135421] [] __dev_queue_xmit+0xef3/0x1c80 [ 31.142178] [] dev_queue_xmit+0x17/0x20 [ 31.148677] [] neigh_resolve_output+0x637/0x790 [ 31.155613] [] ip_finish_output2+0x6ab/0x1110 [ 31.162378] [] ip_do_fragment+0x19cc/0x2190 [ 31.168976] [] ip_fragment.constprop.51+0x143/0x200 [ 31.176275] [] ip_finish_output+0x48a/0xc00 [ 31.182863] [] ip_mc_output+0x233/0x980 [ 31.189109] [] ip_local_out+0x9b/0x180 [ 31.195260] [] ip_send_skb+0x3c/0xc0 [ 31.201242] [] udp_send_skb+0x5c3/0xc60 [ 31.207479] [] udp_sendmsg+0x16c9/0x1c70 [ 31.213800] [] inet_sendmsg+0x203/0x4d0 [ 31.220052] [] sock_sendmsg+0xcc/0x110 [ 31.226213] [] SYSC_sendto+0x21c/0x370 [ 31.232387] [] SyS_sendto+0x40/0x50 [ 31.238282] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 31.245482] [ 31.245482] other info that might help us debug this: [ 31.245482] [ 31.253593] Possible unsafe locking scenario: [ 31.253593] [ 31.259631] CPU0 CPU1 [ 31.264277] ---- ---- [ 31.269000] lock(_xmit_NETROM); [ 31.272658] lock(&(&q->lock)->rlock); [ 31.279365] lock(_xmit_NETROM); [ 31.285545] lock(&(&q->lock)->rlock); [ 31.289727] [ 31.289727] *** DEADLOCK *** [ 31.289727] [ 31.295760] 4 locks held by syz-executor219/3720: [ 31.300577] #0: (rcu_read_lock_bh){......}, at: [] ip_finish_output2+0x212/0x1110 [ 31.310604] #1: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x1d7/0x1c80 [ 31.320478] #2: (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 31.329876] #3: (rcu_read_lock){......}, at: [] dev_hard_start_xmit+0xa8/0x11c0 [ 31.339658] [ 31.339658] stack backtrace: [ 31.344141] CPU: 0 PID: 3720 Comm: syz-executor219 Not tainted 4.4.140-ged9bdc8 #68 [ 31.351907] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 31.361260] 0000000000000000 d43a71df5dd26f41 ffff8800b17fed38 ffffffff81e0e08d [ 31.369272] ffffffff853eb530 ffffffff853ebbf0 ffffffff853eb530 ffff8800b160a150 [ 31.377294] ffff8800b1609800 ffff8800b17fed80 ffffffff8140e6eb 0000000000000003 [ 31.385310] Call Trace: [ 31.387875] [] dump_stack+0xc1/0x124 [ 31.393262] [] print_circular_bug.cold.50+0x1bd/0x27d [ 31.400077] [] __lock_acquire+0x3902/0x5270 [ 31.406021] [] ? debug_check_no_locks_freed+0x210/0x210 [ 31.413013] [] ? trace_hardirqs_on_caller+0x266/0x590 [ 31.419832] [] lock_acquire+0x15e/0x450 [ 31.425433] [] ? ip_defrag+0x318/0x3fe0 [ 31.431035] [] ? inet_frag_find+0x22e/0x9c0 [ 31.436986] [] _raw_spin_lock+0x36/0x50 [ 31.442589] [] ? ip_defrag+0x318/0x3fe0 [ 31.448188] [] ip_defrag+0x318/0x3fe0 [ 31.453629] [] ? debug_check_no_locks_freed+0x210/0x210 [ 31.460621] [] ? memcpy+0x45/0x50 [ 31.465701] [] ? ip_expire+0x770/0x770 [ 31.471221] [] ip_check_defrag+0x3c8/0x7e0 [ 31.477092] [] ? ip_defrag+0x3fe0/0x3fe0 [ 31.482795] [] packet_rcv_fanout+0x52a/0x5e0 [ 31.488828] [] ? packet_bind+0x190/0x190 [ 31.494514] [] dev_hard_start_xmit+0x644/0x11c0 [ 31.500812] [] ? dev_hard_start_xmit+0xa8/0x11c0 [ 31.507214] [] sch_direct_xmit+0x2c1/0x6e0 [ 31.513126] [] ? dev_watchdog+0x7f0/0x7f0 [ 31.518948] [] __dev_queue_xmit+0xef3/0x1c80 [ 31.525014] [] ? __dev_queue_xmit+0x1d7/0x1c80 [ 31.531342] [] ? debug_check_no_locks_freed+0x210/0x210 [ 31.538552] [] ? netdev_pick_tx+0x2c0/0x2c0 [ 31.544516] [] ? memcpy+0x45/0x50 [ 31.549597] [] dev_queue_xmit+0x17/0x20 [ 31.555215] [] neigh_resolve_output+0x637/0x790 [ 31.561520] [] ? ip_finish_output2+0x6ab/0x1110 [ 31.567823] [] ip_finish_output2+0x6ab/0x1110 [ 31.573952] [] ? ip_finish_output2+0x212/0x1110 [ 31.580254] [] ? nf_ct_deliver_cached_events+0x335/0x560 [ 31.587334] [] ? ip_copy_metadata+0x700/0x700 [ 31.593478] [] ip_do_fragment+0x19cc/0x2190 [ 31.599439] [] ? ip_copy_metadata+0x700/0x700 [ 31.605593] [] ip_fragment.constprop.51+0x143/0x200 [ 31.612363] [] ip_finish_output+0x48a/0xc00 [ 31.618348] [] ip_mc_output+0x233/0x980 [ 31.624060] [] ? ip_queue_xmit+0x1af0/0x1af0 [ 31.630470] [] ? ip_make_skb+0x116/0x210 [ 31.636179] [] ? ip_fragment.constprop.51+0x200/0x200 [ 31.643013] [] ? ip_flush_pending_frames+0x30/0x30 [ 31.649587] [] ip_local_out+0x9b/0x180 [ 31.655125] [] ip_send_skb+0x3c/0xc0 [ 31.660477] [] udp_send_skb+0x5c3/0xc60 [ 31.666079] [] udp_sendmsg+0x16c9/0x1c70 [ 31.671777] [] ? ip_reply_glue_bits+0xc0/0xc0 [ 31.677898] [] ? udp4_lib_lookup+0x60/0x60 [ 31.683852] [] ? debug_check_no_locks_freed+0x210/0x210 [ 31.690851] [] ? sock_has_perm+0x1c1/0x400 [ 31.696716] [] ? sock_has_perm+0x29f/0x400 [ 31.702581] [] ? sock_has_perm+0x9f/0x400 [ 31.708367] [] ? inet_sendmsg+0x143/0x4d0 [ 31.714159] [] inet_sendmsg+0x203/0x4d0 [ 31.719756] [] ? inet_sendmsg+0x73/0x4d0 [ 31.725448] [] ? inet_recvmsg+0x4c0/0x4c0 [ 31.731231] [] sock_sendmsg+0xcc/0x110 [ 31.736741] [] SYSC_sendto+0x21c/0x370 [ 31.742257] [] ? SYSC_connect+0x300/0x300 [ 31.748044] [] ? _raw_spin_unlock+0x2c/0x50 [ 31.754006] [] ? do_huge_pmd_anonymous_page+0x38c/0x9d0 [ 31.761000] [] ? handle_mm_fault+0xbf7/0x30b0 [ 31.767127] [] ? SYSC_connect+0x22a/0x300 [ 31.772919] [] ? __do_page_fault+0x385/0xa10 [ 31.778956] [] ? retint_user+0x18/0x3c [ 31.784469] [] SyS_sendto+0x40/0x50 [ 31.789717] [] entry_SYSCALL_64_fastpath+0x22/0x9e