[....] Starting periodic command scheduler: cron[?25l[?1c7[1G[[32m ok [39;49m8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 20.552345] 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: [ 21.982174] random: sshd: uninitialized urandom read (32 bytes read, 34 bits of entropy available) [ 22.406595] random: sshd: uninitialized urandom read (32 bytes read, 35 bits of entropy available) [ 23.805238] random: sshd: uninitialized urandom read (32 bytes read, 116 bits of entropy available) [ 23.963593] random: sshd: uninitialized urandom read (32 bytes read, 118 bits of entropy available) Warning: Permanently added '10.128.15.201' (ECDSA) to the list of known hosts. [ 29.468798] random: sshd: uninitialized urandom read (32 bytes read, 124 bits of entropy available) net.ipv6.conf.syz_tun.accept_dad = 0 [ 29.563999] IPVS: Creating netns size=2552 id=1 net.ipv6.conf.syz_tun.router_solicitations = 0 executing program [ 29.657136] [ 29.658788] ====================================================== [ 29.665079] [ INFO: possible circular locking dependency detected ] [ 29.671455] 4.4.140-ged9bdc8 #68 Not tainted [ 29.675853] ------------------------------------------------------- [ 29.682238] syz-executor772/3808 is trying to acquire lock: [ 29.687932] (&(&q->lock)->rlock){+.-...}, at: [] ip_defrag+0x318/0x3fe0 [ 29.696830] [ 29.696830] but task is already holding lock: [ 29.702782] (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 29.711576] [ 29.711576] which lock already depends on the new lock. [ 29.711576] [ 29.719871] [ 29.719871] the existing dependency chain (in reverse order) is: [ 29.727470] -> #1 (_xmit_NETROM){+.-...}: [ 29.732270] [] lock_acquire+0x15e/0x450 [ 29.738531] [] _raw_spin_lock_irqsave+0x4e/0x70 [ 29.745472] [] depot_save_stack+0x211/0x610 [ 29.752064] [] save_stack+0xa9/0xd0 [ 29.757965] [] kasan_kmalloc+0xc7/0xe0 [ 29.764118] [] kasan_slab_alloc+0x12/0x20 [ 29.770533] [] kmem_cache_alloc+0xbe/0x2a0 [ 29.777041] [] inet_getpeer.part.5+0xeac/0x15a0 [ 29.783984] [] inet_getpeer+0x55b/0x6f0 [ 29.790225] [] icmp6_send+0x17c5/0x1b80 [ 29.796491] [] icmpv6_param_prob+0x29/0x40 [ 29.802987] [] ipv6_frag_rcv+0x3f94/0x4fd0 [ 29.809487] [] ip6_input_finish+0x32e/0x1550 [ 29.816164] [] ip6_input+0xf6/0x200 [ 29.822052] [] ip6_rcv_finish+0x13d/0x640 [ 29.828464] [] ipv6_rcv+0x10cb/0x1cd0 [ 29.834545] [] __netif_receive_skb_core+0x12d6/0x2940 [ 29.842010] [] __netif_receive_skb+0x5b/0x1b0 [ 29.849030] [] process_backlog+0x216/0x6a0 [ 29.855530] [] net_rx_action+0x3a2/0xdb0 [ 29.861846] [] __do_softirq+0x22c/0xa1a [ 29.868084] [] do_softirq_own_stack+0x1c/0x30 [ 29.874933] [] do_softirq.part.16+0x54/0x60 [ 29.881513] [] do_softirq+0x19/0x20 [ 29.887407] [] netif_rx_ni+0xec/0x3a0 [ 29.893489] [] tun_get_user+0xbe7/0x2410 [ 29.899823] [] tun_chr_write_iter+0xd5/0x190 [ 29.906492] [] do_iter_readv_writev+0x13c/0x1e0 [ 29.913429] [] do_readv_writev+0x2e0/0x6e0 [ 29.919927] [] vfs_writev+0x7b/0xb0 [ 29.925821] [] SyS_writev+0xd9/0x250 [ 29.931820] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 29.939010] -> #0 (&(&q->lock)->rlock){+.-...}: [ 29.944301] [] __lock_acquire+0x3902/0x5270 [ 29.950891] [] lock_acquire+0x15e/0x450 [ 29.957152] [] _raw_spin_lock+0x36/0x50 [ 29.963397] [] ip_defrag+0x318/0x3fe0 [ 29.969553] [] ip_check_defrag+0x3c8/0x7e0 [ 29.976055] [] packet_rcv_fanout+0x52a/0x5e0 [ 29.982725] [] dev_hard_start_xmit+0x644/0x11c0 [ 29.989663] [] sch_direct_xmit+0x2c1/0x6e0 [ 29.996160] [] __dev_queue_xmit+0xef3/0x1c80 [ 30.002837] [] dev_queue_xmit+0x17/0x20 [ 30.009083] [] neigh_resolve_output+0x637/0x790 [ 30.016014] [] ip_finish_output2+0x6ab/0x1110 [ 30.022772] [] ip_do_fragment+0x19cc/0x2190 [ 30.029354] [] ip_fragment.constprop.51+0x143/0x200 [ 30.036646] [] ip_finish_output+0x48a/0xc00 [ 30.043237] [] ip_mc_output+0x233/0x980 [ 30.049590] [] ip_local_out+0x9b/0x180 [ 30.055753] [] ip_send_skb+0x3c/0xc0 [ 30.061735] [] udp_send_skb+0x5c3/0xc60 [ 30.067985] [] udp_sendmsg+0x16c9/0x1c70 [ 30.074309] [] inet_sendmsg+0x203/0x4d0 [ 30.080562] [] sock_sendmsg+0xcc/0x110 [ 30.087245] [] SYSC_sendto+0x21c/0x370 [ 30.093405] [] SyS_sendto+0x40/0x50 [ 30.099300] [] entry_SYSCALL_64_fastpath+0x22/0x9e [ 30.106495] [ 30.106495] other info that might help us debug this: [ 30.106495] [ 30.114608] Possible unsafe locking scenario: [ 30.114608] [ 30.120640] CPU0 CPU1 [ 30.125282] ---- ---- [ 30.129919] lock(_xmit_NETROM); [ 30.133608] lock(&(&q->lock)->rlock); [ 30.140307] lock(_xmit_NETROM); [ 30.146572] lock(&(&q->lock)->rlock); [ 30.150760] [ 30.150760] *** DEADLOCK *** [ 30.150760] [ 30.156795] 4 locks held by syz-executor772/3808: [ 30.162218] #0: (rcu_read_lock_bh){......}, at: [] ip_finish_output2+0x212/0x1110 [ 30.172173] #1: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x1d7/0x1c80 [ 30.182034] #2: (_xmit_NETROM){+.-...}, at: [] sch_direct_xmit+0x23c/0x6e0 [ 30.191450] #3: (rcu_read_lock){......}, at: [] dev_hard_start_xmit+0xa8/0x11c0 [ 30.201207] [ 30.201207] stack backtrace: [ 30.205683] CPU: 1 PID: 3808 Comm: syz-executor772 Not tainted 4.4.140-ged9bdc8 #68 [ 30.213447] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 30.222775] 0000000000000000 a739b9ebca0f6e17 ffff8800ae2d6d38 ffffffff81e0e08d [ 30.230822] ffffffff853eb890 ffffffff853ebf50 ffffffff853eb890 ffff8801c985e950 [ 30.238823] ffff8801c985e000 ffff8800ae2d6d80 ffffffff8140e6eb 0000000000000003 [ 30.246815] Call Trace: [ 30.249657] [] dump_stack+0xc1/0x124 [ 30.254996] [] print_circular_bug.cold.50+0x1bd/0x27d [ 30.261808] [] __lock_acquire+0x3902/0x5270 [ 30.267763] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.274749] [] ? trace_hardirqs_on_caller+0x266/0x590 [ 30.281566] [] lock_acquire+0x15e/0x450 [ 30.287170] [] ? ip_defrag+0x318/0x3fe0 [ 30.292774] [] ? inet_frag_find+0x22e/0x9c0 [ 30.299164] [] _raw_spin_lock+0x36/0x50 [ 30.304760] [] ? ip_defrag+0x318/0x3fe0 [ 30.310381] [] ip_defrag+0x318/0x3fe0 [ 30.315801] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.322786] [] ? memcpy+0x45/0x50 [ 30.327954] [] ? ip_expire+0x770/0x770 [ 30.333461] [] ip_check_defrag+0x3c8/0x7e0 [ 30.339318] [] ? ip_defrag+0x3fe0/0x3fe0 [ 30.345009] [] packet_rcv_fanout+0x52a/0x5e0 [ 30.351036] [] ? packet_bind+0x190/0x190 [ 30.356719] [] dev_hard_start_xmit+0x644/0x11c0 [ 30.363013] [] ? dev_hard_start_xmit+0xa8/0x11c0 [ 30.369395] [] sch_direct_xmit+0x2c1/0x6e0 [ 30.375249] [] ? dev_watchdog+0x7f0/0x7f0 [ 30.381017] [] __dev_queue_xmit+0xef3/0x1c80 [ 30.387045] [] ? __dev_queue_xmit+0x1d7/0x1c80 [ 30.393276] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.400280] [] ? netdev_pick_tx+0x2c0/0x2c0 [ 30.406370] [] ? memcpy+0x45/0x50 [ 30.411444] [] dev_queue_xmit+0x17/0x20 [ 30.417039] [] neigh_resolve_output+0x637/0x790 [ 30.423381] [] ? ip_finish_output2+0x6ab/0x1110 [ 30.429670] [] ip_finish_output2+0x6ab/0x1110 [ 30.435790] [] ? ip_finish_output2+0x212/0x1110 [ 30.442085] [] ? nf_ct_deliver_cached_events+0x335/0x560 [ 30.449163] [] ? ip_copy_metadata+0x700/0x700 [ 30.455280] [] ip_do_fragment+0x19cc/0x2190 [ 30.461316] [] ? ip_copy_metadata+0x700/0x700 [ 30.467463] [] ip_fragment.constprop.51+0x143/0x200 [ 30.474106] [] ip_finish_output+0x48a/0xc00 [ 30.480050] [] ip_mc_output+0x233/0x980 [ 30.485645] [] ? ip_queue_xmit+0x1af0/0x1af0 [ 30.491672] [] ? ip_make_skb+0x116/0x210 [ 30.497366] [] ? ip_fragment.constprop.51+0x200/0x200 [ 30.504185] [] ? ip_flush_pending_frames+0x30/0x30 [ 30.510778] [] ip_local_out+0x9b/0x180 [ 30.516292] [] ip_send_skb+0x3c/0xc0 [ 30.521649] [] udp_send_skb+0x5c3/0xc60 [ 30.527270] [] udp_sendmsg+0x16c9/0x1c70 [ 30.532957] [] ? ip_reply_glue_bits+0xc0/0xc0 [ 30.539072] [] ? udp4_lib_lookup+0x60/0x60 [ 30.544940] [] ? debug_check_no_locks_freed+0x210/0x210 [ 30.551925] [] ? sock_has_perm+0x1c1/0x400 [ 30.557787] [] ? sock_has_perm+0x29f/0x400 [ 30.563643] [] ? sock_has_perm+0x9f/0x400 [ 30.569416] [] ? inet_sendmsg+0x143/0x4d0 [ 30.575213] [] inet_sendmsg+0x203/0x4d0 [ 30.580830] [] ? inet_sendmsg+0x73/0x4d0 [ 30.586545] [] ? inet_recvmsg+0x4c0/0x4c0 [ 30.592345] [] sock_sendmsg+0xcc/0x110 [ 30.597891] [] SYSC_sendto+0x21c/0x370 [ 30.603437] [] ? SYSC_connect+0x300/0x300 [ 30.609218] [] ? _raw_spin_unlock+0x2c/0x50 [ 30.615181] [] ? do_huge_pmd_anonymous_page+0x38c/0x9d0 [ 30.622195] [] ? handle_mm_fault+0xbf7/0x30b0 [ 30.628324] [] ? SYSC_connect+0x22a/0x300 [ 30.634101] [] ? __do_page_fault+0x385/0xa10 [ 30.640133] [] ? retint_user+0x18/0x3c [ 30.645646] [] SyS_sendto+0x40/0x50 [ 30.650894] [] entry_SYSCALL_64_fastpath+0x22/0x9e